CA1136068A - Discharge electrode - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The specification describes a discharge electrode adapted for use in an electrostatic precipitator for propagation of corona discharge. The discharge electrode includes an elongated electrode assembly having an elongated support means which is substantially longitudinally coextensive with at least a major portion of the longitudinal extent of the electrode assembly and is located laterally intermediate a pair of laterally spaced apart longitudinal side portions of the assembly and wherein at least one of the side portions is of a form to permit corona discharge therefrom. The electrode assembly comprises a pair of elongated formed body elements each substantially coextensive with the electrode assembly. Each of the body elements includes a pair of laterally spaced apart edge portions longitudinally coextensive therewith and an elongated formed intermediate portion substantially coextensive therewith and spaced laterally from at least one of the pair of edge portions. The pair of body elements are disposed with respect to each other and fixedly secured together to form the electrode assembly in a manner that the at least one edge portion of the body element forms the laterally outermost extent of a respective one of the side portions and the respective formed intermediate portions of the body elements cooperate to form the elongated support means. At least one of the body elements includes formed corona discharge means extending longitudinally adjacent at least one edge portion thereof and spaced laterally from the elongated support means.

Description

~136068 .... .
This is a division of Canad.ian Application 300,045 filed rSarch 30, 1978.
In the art of gas cleansing by e~ectrostatic precipitation it is well known to provide'laterally spaced apar~ and oppos~teIy charged discharge and'collector electrode means within an electrostatic precipitator for, the purpose of arresting particulate matter from a stxeam of gas passed therethrough.' Among conventlonal discharge electrode means are the so-called pole or mast type electrodes which typica~ly have been chaxacteriæed by their .: .
- elongated, fonmed structure inc~uding variously oxmed protrusions thereon to promote efficient corona discharge, for ~Kample as shown in U.S. patents 3,985,524, ~,200,56~' 3,616,608, 3,~58,453, 3,158,454 and 3,25?,779 among many others.
Al~hough known mas~ or pole type dLs~ha~ge electrodes have'generally ser~ed ~he intended purpo~e~ ~hey have neverthe~ess often been subiect to serîous deficien-cies. For example, conventional electrode structures and particularly those formed in re~atively thin sheet metal of~en have been subject to considerable lateral defleetion as a result of periodic rapping or by their tendency to act as airfoils thus causing a pressure differentlal in the 'gas flowing at high velocity over the electrode. Excessiv~
electrode deflection may result in,arcing between adjacent discharge and collector electrodes thereby degrading dust collecting efficiency or causing localized burning of the electrodes. In the prior art, the requisi~e structural rigidity in such electrodes has been provided by such means as the use of heavier gauge sheet metal than would other-wise be required or by af~ixing additional structural members to the electrode.' This approach seriously ~k ~ 2- .

113606~3 complicates electrode fabrication, results in unduly heavy and cumbersome electrodes and is unnecessarily wasteful of materials. Additionally, many prior mast or pole type discharge electrodes have included integrally formed stiffener means adjacent the electrode edges from which corona discharge emanates. Thus the design con-siderations for desirable corona discharge and for required structural rigidity have often been in conflict and the difficulty of optimizing the electrode design has been correspondingly increased.
Furthermore, the formed protrusions on prior electrodes constitute, in effect, point sources of corona emission whereby the resulting distribution of corona emission over the length of the electrode is quite non-uniform.
These and other deficiencies of prior mast type discharge electrodes are alleviated by the present invention according to which there is provided an elongated, formed discharge electrode having support or stiffener means formed integral therewith intermediate the corona emitting electrode edge portions. The electrode of this invention additionally offers improved corona propagating means and enhanced durability and simplicity of fabrication.
In accordance with the present invention, therefore, there is provided a discharge electrode adapted for use in an electrostatic precipitator for propagation of corona discharge.
The discharge electrode includes an elongated electrode assembly having an elongated support means which is substantially longitudinally coextensive with at least a major portion of the longitudinal extent of the electrode assembly and is located laterally intermediate a pair of laterally spaced apart longitudinal side portions of the csm ~

1136(~68 assembly and wherein at least one of the side portions is of a form to permit corona discharge therefrom. The electrode assembly comprises a pair of elongated formed body elements each substantially coe~tensive with the electrode assembly. Each of the body elements includes a pair of laterally spaced apart edge portions longitudinally ~` coextensive therewith and an elongated formed intermediate portion substantially coextensive therewith and spaced laterally from at least one of the pair of edge portions.
The pair of body elements are disposed with respect to each other and fixedly secured together to form the electrode assembly in a manner that the at least one edge portion of the body element forms the laterally outermost extent of a respective one of the side portions and the respective formed intermediate portions of the body elements cooperate to form the elongated support means. At least one of the body elements includes formed corona discharge means extending longitudinally adjacent at least one edge portion thereof and spaced laterally from the elongated support means.
These and other objects and advantages of the invention are more fully specified in the following description with reference to the accompanying figures, in which:
Fig. 1 is a schematic cross section of an electrostatic precipitator including discharge electrode means of the present invention;

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1~36068 Fig. 2 is an enlarged fragmentary portion of Fig. 1 showing an upper end portion of a discharge electrode according to one preferred embodiment of the invention;
Fig. 3 is a transverse section of the electrode of Fig. 2 taken on line III-III of Fig. 2;
Fig. 4 is a transverse section similar to Fig. 3 showing a variation of the embodiment of Fig. 3;
Fig. 5 is a transverse section similar to Figs. 3 and 4 showing yet another variation of the embodiment of Fig. 3;
Fig. 6 is a partial side elevation taken on line VI-VI of Fig. 5;
Fig. 7 is a partial side elevation of another preferred embodiment of the invention;
Fig. 8 is an elevation taken on line 8-8 of Fig. 7;
Fig. 9 is a transverse cross section taken on line 9-9 of Fig. 7; and Fig. 10 is an elevation similar to Fig. 7 showing a variation of the embodiment of Fig. 7;
~here is generally indicated at 10 in Fig. 1 an electrostatic precipitator including discharge electrode means. Certain aspects of the discharge electrode means as disclosed herein are disclosed and claimed in copending Canadian Application Serial Number 300,045, filed March 30, 1978. For purposes of illustration the precipitator 10 is shown in simplified schematic form and of course it is to be understood from the outset that such simplification is not intended to unduly limit the scope of the invention 3~ described.

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Precipitator 10 comprises a closed housing 12 which encloses a space 14 and includes gas inlet and outlet means 24, 26, respectively, whereby a flow of gas ma~ be directed through space 14 as indicated by arrows 28 for cleansing. Within space 14 there is carried at least one discharge elec~rode bank 21 assembled from a plurality of discharge electrodes 20. Electrodes 20 are carried in generally verticalLy extending, parallel orien~cation by respective pairs o~ upper ~nd ~ower ele~
~rode support members 15, 30 such tha~ ~he electrodes ~0 . extend transversely across t~e gas flow path with ~he plane of each electrode 20 ~enerally aligned wi~h ~he direc~ion o~ gas flow. Members 15, 30 supportingly and electrically conduc~ively engage respective upper and lower end portions o the electrodes 20. Th~ upper suppo~t mem~ers 15 are suitably secured to a rigid support frame 16. Frame 16 in turn is carried by and electrically insulated from housing ~2 as by an elongated upwardly extending frame hanger member 17 which is supportingly engaged by a well known compression insulator 18 such that frame 16 and the electrode bank 21 carried thereby are suspended within the flow path of gas passed through space 14. Adjacent the lower ends of respective electrodes 20, the lower support memebrs 30 are suitably secured to a base frame 22 which is electrically insulated from hous-ing 12 as by the surrounding air space.
As is well known, there may be provided a plurality of generally parallel, laterally spaced electrode banks 21 within space 14 with conventional grounded collector electrode plates 23 also carried within 1136~)68 .

space 14 intermediate respective pairs of adj acent discharge electrode banks 21 and parallel theret'o whereby the'discharge electrodes 20 may be electrically energized' by a~y suitable means (not shown) to set up corona discharge therefrom in the'space between each discharge electrode 20 and the respective adjacent coLlecto~s 23, Accordingly, in practice'the'gas stream passed through ~pace 14 is cleansed by electrical precipitation of . entrained particulate contaminan~s and deposition ~hereof on the collector electrode plates 23 in ~he we~l known manner. Con~en~ional sapping ~echniques are employed to dislodge the accumulatad contaminants from collec~or electrodes 23 ~or disposal. ~nasmuch as electros~atic precipitators-such as descr~bed hereinabove'and ~he ' ' . .operation ~hereo are well known ~o ~hose versed in the art, ~urther'detailed description thereo~ i~ considered unnecessary for an understanding o the present invenion.
According to one preferred embodiment o the ~ ~nvention as shown in Figs. 2 and 3, each electrode 20 ~ncludes a~ elongated, generally planar and substantially ' unitary electrode body 36 formed as by roll forming or similar processes and comprising:. a central axially , . e~tending elongated stifener or support portion 38 ~ormed intermediate the transversely opposed longitudinal edges 58 of the body 36 and corona discharge portions shown as ' elongated tabs 40 ormed adjacent respective adges 58 ~o ' ' deine respective lines o corona e~ission extending therealong, Supporting web portions 42 extend inter-mediate respective-tabs 40 and stiffener portion 38. The electrode portions 38, 40 and.42 ordinarily may be '`' 1~ 3 6 0 6 8 coextensive throughout substantially the entire'length of body 36.
StiL~fener portion 38 is so formed ~s ~o define a longitudinally extending opening 50 substantially co-extensive therewith. The'opening 50, shown as having a circular cross sec~ion, is adapted ~o have'secured therewithin the cooperably formed support members~l5 and 30 adjacent respective opposed end portions of body 36 (only the upper end portion is shown in Fig. 2) as by weld-ments 60 whereby members 15 and 30 are eIectrically con-duc~ivèly affixed to bod~ 36. As sho~n in Figs. 2 and 3, body 36 is comprised of two identical and generally planar elongated, formed plates 44, each being formed for example from No. 16 g~uge s~eel to have a thickness of approxima~ely 0.04 to 0.08 inches ~ach plate 44 includes a longitudinally extending semi-circular outward bend 48 intermediate the longi~udinal edges thereof which forms one half of the stiffener portion 38, and a plurality of'the longitudinally spaced tabs 40 transversely to one side of bend 48 adjacent one longitudinal edge of each plate 44. In each plate 44, a longitudinal web portion 42a extends transversely intermediate the bend 48 and tabs 40, and a second elongated web portion 42b extends transversely outward from bend 48 generally coplanar with and in the opposite direction from web 42a.
In assembly, two plates 44 are positioned adjacent one another so as to extend in generally parallel coplanar relation with the inner or concave sides of the bends 48 coaxially aligned and facing each'other, and with'the tabs 40 of each plate 44 being spaced laterally in opposite .` : ?136068 directions as shown in Fig. 3. The two plates 44 are affixed rigidly together in the'position des'cribed as by a plurality of resis~ance weIdments 52 spaced longitudinally at intervals to rigidly secure'together adjacent web poxtions 42a and'42b such'that the iuxtaposed outward bends 48 form the stiffener.portion 38 and opening 50. 0 course, any suitable alternative fastening means may be employed in lieu weldments 52, for example ot~er types of welding, threaded fasteners or rivets.
Longitudinally ad~acent ones of tabs 40 are shown as being formed by intervening s~ots 39 and as shown may be bent or outstruck alternately in opposite directions rom the plane o~ web portion 42 at an angle . of approx~mately 45 degrees, for example such that alter-nate tabs 40 provide corona emission to the collector plates 23 on opposite sides of the discharge electrode 20.
Of course, the particular angle, shape and size o tabs 40 may be varied to achieve the most desirable and efficient pattern of corona emission therefrom. For example, in another preferred embodiment of ~his invention which is described in detail heréinbelow tabs 40 may be substantially coplanar with web 42 such that - corona will propagate from each tab to the collector plates 23 on both sides of the discharge electrode. In any case, one desirable property in the discharge electrode of this invention is that the pattern of corona discharge to collectors on opposite sides of the discharge electrode be generally symmetrical about the plane of the discharge electrode. By this it is meant that approximately equal corona discharge propagates from one edge of the electrode ~136~)~i8 20 to each of the ad;acent collector electrodes 23.
Fig. 4 illustrates a variation of the embodiment of Figs. 2 and 3 wherein eIectrode body 36 is comprised of a generally planar elongated formed plate 44' having a formed semi-circular outward bend 48' which extends longitudinally of plate'44' and is located centrally intermediate opposed longitudinal edges 58 thereof. Corona discharge means such as outstruck tabs 40 are formed adjacen~ the edges 58 of plate'44' and identi~al coplana~ web port~ons 42' extend inter-mediate the bend 48' and respective tabs 40. A~cor~ng to this embodiment an elongated s~iffener por~ion 3~', including an elongated cylindrical opening S0' adapted to receive suppor~ members lS and 30, is formed by bend 48 in cooperation with an elongated, formed means shown as a member 54 having an elongated semi-circular outward bend 62 formed intermediate transversely extending coplanar web portions 64 thereof. The members 44' and 54 are positioned with the respective inner or concave sides o~
bends 48' and 62 facing each other and coaxially aligned to form the stiffener portion 38' and opening S0' in the manner indicated hereinabove for the first described ~mbodiment, and the respective web portions 64 and 42' are affixed rigidly together in any suitable manner as ~ereinabove described to form the substantially unitary body 36'. Elongated means 54 may be comprised of a plurality of distinc~ members affixed at longitudinally spaced intervals along the member 44' if desired.
Another variation on the embodiment of Figs. 2 and 3 is shown in Figs. 5 and 6 wherein electrode body 36''' 1136~368 comprises a single, elongated, generally planar forned member 44''having an elongated stiffener portion 38'' and identical9 coplanar web por~ions 42'' extending transversely in opposite directions therefrom. Tabs 40 are formed adjacent respective opposed outer edges 58 of member 4411. According to this embodiment, a cylindrical opening 50' ' to receive support members 15 and 30 is formed by a plurality of longitudinal~y adjacent segments 66 of stifener portion 38'' being outwardly formed alternately in opposite directions.
In each of ~he hereinabo~e and hereillbelow described varia~io~s, the stiffener portions 38-381' are suitably formed and dimensioned to provide the struct~ral rigidity considered suff1cient to render ~he electrode body 36-36'' substantially se~-supporting in that` only the end support members 15 and 30 are needed to support ~he electrode and that portion of the electrode body extending longit~dinally intermediate the respective electrode body ends has no support means other than its own formed structure. The openings 50-50'' as - described may be 6ubstantially coextensive with stiffeners 38-38'' whereby if desired the support members 15 and 3Q
may be longitudinally opposed end portions of a single elongated member disposed within the opening 50 and extend-ingthrouhgout thelength of body 36 to provide added struc-tural rigidity therefor. If members 15 and 30 engage only the opposed end portions of the body 36, the stiffener portion 38 intermediate the end portions engaging members 15 and 30 need not necessarily be formed to include the openin~ 50, for example as in the hereinbelow described 11 3 6~ 6 8 embodiment.
In Figs. 7, 8 and 9, there is shown another preferred embodiment of the invention wherein the electrode body 36''' includes a formed plate member 70 having a generally serpentine or S-curved longitudinally extending stiffener portion 72 formed laterally intermediate the longitudinal edges 74 thereof. Generally coplanar side - portions 76 of plate 70 are spaced laterally to eithe~
side of st~ffener portion 72 and Pach has formed thexein corona discharge means such as a plura~ity of longitudinally spaced tabs 78 and inter~ening notches 8Q. The coron~
discharge tabs 78 may be coplanar with each other and with side portions 76 as shown or may be alternately outstruck as described hereinbelow. The dimensions and spacing of notches 80 may be varied to alter the current-voltage characteristics and hence the corona discharge charac~eris-tics of the electrode. For example, it may be desirable that the electrode 20 ha~e a current-voltage characteristic approximating ~hat of a pair of laterally spaced, parallel-wire discharge electrodes. One suitable configuration is shown in Fig. lO wherein the longitudinal extent of tabs 78 is approximately equal ~o the longitudinal extent ofnotches 80. A similar configuration results from the tabs in the embodiment of Fig. 3 being of substantially equal longitud-inal extent and being outstruck in opposite directions. It should be noted, however, that in general the longer the notches 80 are in relation to the length of the tabs 78, the more corona propagation from the electrode will deviate from longitudinal uniformity. As notches 80 are lengthened and tabs 78 correspondingly shortened, the corona . ` il36~68 propagation pattern will approach that of plural, longitudinally spaced discharge points. In a variation of the Fig. 10 con~iguration (not shown) ~he alterna.te - notches 80 and tabs 78 formed in the opposite edges 7~ of plate 70 may be longitudlnaily offset or staggered ln such a manner that each tab 78 in one edge 74 is transversely aligned with a notch 80 formed in the opposite - edge 74. In an alternate embodiment the ~orona discharge means may be comprised of a continuous edge portion o~ the discharge elect~ode having no cutouts or notches therein.
corona emi.ssion from the disch~r~e elect-~odes must be cur~ailed, as for example.to promote the uniform current flow or corona discharge to the collectors near the upper and lower ends of the body 36 whereat edgeg 74 are disposed laterally adjacent corresponding edge portions of collector plates 23, electrically conductive shroud means 82 may be employed as shown to 'isoften" the contour of the elctrode thereat by eliminating exposed edge por-tions and curtailing corona discharge from the covered edge portions. As shown, shrouds 82 may b~ formed as elongated, generally tubular members each having a longitudinally `
exten~ing through slot 84 which receives the edge 74 of plate 70 whereby the edges of slit 84 grip plate 7Q
to secure the shroud 82 thereto.
The formed plate member 70 extends intermediate frames 16, 22 and is secured thereto by respective upper and lower support members 15', 30'. As shown, member lS' comprises a formed body having a transversely extending upper body portion 86 by which t~e support 15' is releas-ably secured to a cooperably formed lower portion 88 of frame 16 as by threaded fasteners 90, and a pair of inwardly and downwardly converging side portions 92 ~he lower ends of which receive ~he respec~ive upper ends of e~.ectrode side portions 76 therebetween for securing thereof as by threaded fasteners 94. In similar ~ashion an upwardly extending end portion 96 of generally H-shaped, elongated, lower alignment support.-30' is secured by . threaded fasteners 98 to the lower ends of respective electrode side portions 7~, and t~e lower end of suppor~
30' is secured by ~hreaded fasteners 100 ~o frame-22.
- According to the description hereinabove, there is provided by the instant invention an improved discharge electrode of the pole or mast type for electrostatic precipitators which is uncomplicated in fabrication and assembly, hlghly durable and su~ficiently rigid by virtue of integrally formed stiffener portions therein to resist excess lateral deflections without being wasteful of materials in fabrication.
Although only certain preferred embodments of the invention have been described herein it is to be under-stood that the invention may be practiced in numerous alternative embodiments with various modifications thereto without departing from the broad spirit and scope thereof.
For example: openings may be formed in web portions 42 to provide a lighter weight electrode assembly; the support members 15 and 30 may comprise tubular members or solid bars of any suitable cross section with the cross section of respecti~e openings 50 being cooperably formed; the tabs 40 may be formed and positioned according to any of numerous suitable desi~ns, for example, a sawtooth -13- .

1136()68 configuratiorl; the electrodes may be assembled from plural elongated clectrode portions connected end to end; an electrodc may co~)ine elements of the several described embodiments in a single structure. These and other embodiments and modifications have been envisioned and anticipated by the inventor, this invention should be interpreted as broadly as permitted by the scope of the claims appended hereto.

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Claims (12)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a discharge electrode adapted for use in an electrostatic precipitator for propagation of corona discharge wherein said discharge electrode includes an elongated electrode assembly having an elongated support means which is substantially longitudinally coextensive with at least a major portion of the longitudinal extent of said electrode assembly and is located laterally intermediate a pair of laterally spaced apart longitudinal side portions of said assembly and wherein at least one of said side portions is of a form to permit corona discharge therefrom, said electrode assembly comprising: a pair of elongated formed body elements each substantially coextensive with said electrode assembly; each of said body elements including a pair of laterally spaced apart edge portions longitudinally coextensive therewith and an elongated formed intermediate portion substantially coextensive therewith and spaced laterally from at least one of said pair of edge portions;
said pair of body elements being disposed with respect to each other and fixedly secured together to form said electrode assembly in a manner that said at least one edge portion of each said body element forms the laterally outermost extent of a respective one of said side portions and the respective formed intermediate portions of said body elements cooperate to form said elongated support means;
and at least one of said body elements including formed corona discharge means extending longitudinally adjacent said at least one edge portion thereof and spaced laterally from said elongated support means.

2. A discharge electrode assembly as claimed in claim 1 wherein said corona discharge means includes longitudinally extending pluralities of elongated tabs and intervening notches.

3. A discharge electrode assembly as claimed in claim 2 wherein said corona discharge means is substantially symmetrical with respect to a plane aligned with the lateral extent of the respective said at least one of said side portions.

4. A discharge electrode assembly as claimed in claim 3 wherein alternate ones of said tabs are outstruck to opposite sides of said plane.

5. A discharge electrode assembly as claimed in claim 4 wherein the longitudinal extent of at least some of said tabs is at least as great as the longitudinal extent of one of the respective said intervening notches longitudinally adjacent thereto.

6. A discharge electrode assembly as claimed in claim 5 wherein said at least some of said tabs is a majority of said tabs.

7. A discharge electrode assembly as claimed in claim 1 wherein said elongated support means is of a generally circular cross sectional form.

8. A discharge electrode assembly as claimed in claim 7 wherein said formed intermediate portion of each of said body elements includes a longitudinally extending generally semi-circular bend in the respective said body element.

9. A discharge electrode assembly as claimed in claim 1 wherein said body elements are substantially identical.

10. A discharge electrode assembly as claimed in claim 2 wherein said corona discharge means and the respective said at least one of said side portions are substantially coplanar.

11. A discharge electrode assembly as claimed in claim 1 wherein said corona discharge means and said formed intermediate portion are formed integrally with the respective said body elements.

12. A discharge electrode assembly as claimed in claim 1 additionally including shroud means removably secured thereto adjacent selected longitudinal extents of said corona discharge means for curtailing corona discharge therefrom.