US3793804A

US3793804A - Collector electrode for electrostatic precipitator

Info

Publication number: US3793804A
Application number: US00244659A
Authority: US
Inventors: W Steuernagel
Original assignee: Metallgesellschaft AG
Current assignee: GEA Group AG
Priority date: 1971-04-20
Filing date: 1972-04-17
Publication date: 1974-02-26
Anticipated expiration: 1991-02-26
Also published as: GB1358123A; CS164920B2; DE7114982U; JPS551102B1; RO59485A

Abstract

A collector electrode for an electrostatic precipitator in the form of a sheet-metal strip reinforced by a channel structure in which the corrugations are in the form of flat trapezoid sections with open broad bases turned in opposite direction and running along the length of the strip. The strips have overlapping flanges where they adjoin and comprise at least three such trapezoidal sections.

Description

United States Patent 11 9] Steuernagel Feb. 26, 1974 COLLECTOR ELECTRODE FOR 2,946,400 7/1960 Gustafsson 55/130 ELECTROSTATIC PRECIPITATOR 3,282,029 11/1966 Steuemagel 3,418,792 12/1968 Quintilian et a1. 55/156 [75] Inventor: Walter Steuernagel, Frankfurt/Mam,

Germany FOREIGN PATENTS OR APPLICATIONS [73] Assignee: Metallgesellschaft Aktiengesellschaft, 747,301 4/1956 Great Britain 55/130 Frankfurt am Main Germany 963,109 7/1964 Great Britain 55/130 138,721 l/l953 Sweden 55/130 [22], Filed: Apr. 17, 1972 [21] Appl. No.: 244,659 Primary Examiner-Dennis E. Talbert, Jr.

Related U S. Application Data Attorney, Agent, or Firm-Karl F. Ross; Herbert [63] Continuation-impart of Ser. No. 154,086, June 17, Dllbno [30] Foreign Application Priority Data [57] ABSTRACT Germany G 7] l4 A collector electrode for an electrostatic precipitator in the form of a sheet-metal strip reinforced by a 55/112 55/ channel structure in which the corrugations are in the 58] Fie'ld 148 154 form of flat trapezoid sections with open broad bases 5 turned in opposite direction and running along the length of the strip. The strips have overlapping flanges [56] References Cited where they adjoin and comprise at least three such trapezoidal sections. UNITED STATES PATENTS 1,345,790 7/1920 Lodge 55/129 X 8 Claims, 4 Drawing Figures HV l5 COLLECTOR ELECTRODE FOR ELECTROSTATIC PRECIPITATOR CROSS-REFERENCE TO RELATED APPLICATION The'present application is a continuation-in-part of my application No. 154,086, filed June 17, 1971 and entitled COLLECTOR ELECTRODE FOR ELEC- TROSTATIC PRECIPITATOR.

FIELD OF THE INVENTION The present invention relates to electrostatic precipitators, filters and like particle-removing apparatus and, more particularly, to a collector-electrode arrangement for an electrostatic precipitator.

BACKGROUND OF THE INVENTION In general, an electrostatic precipitator comprises an electrode system including corona-discharge electrodes and collector electrodes, the latter being spaced apart to define channels for a fluid traversing the system. Means are provided for inducing a gas flow through the precipitator and along the electrode system and means may be provided for removing the collected particles. The latter means may include a rapping device for imparting impulsive shocks to the collector electrodes thereby causing any accumulated materials to fall into collector bins or the like.

The corona discharge generated at the discharge electrodes, ionizes the gases and an electric charge is thereby imparted to the solid particles contained therein, which particles cannot readily be removed by filtering, sedimentation and other methods. The particles are attracted to and tend to accumulate upon the collector electrodes which have an opposite charge and induce adhesion by electrostatic forces. Sometimes the electrostatic precipitator follows or is downstream of a mechanical separator in which particles of larger size are recovered.

In modern electrostatic precipitators, having collector electrode surface areas from several thousand square meters to 10,000 m it is necessary to provide high stability of shape of the collector electrodes at low cost. For example, the collector-electrode strips may be joined together contiguously along their longitudinal edges to form collector electrodes having a height of 8 to 12 meters and a relatively close spacing, the coronadischarge electrodes being arrayed between the cllector electrodes.

The particle-containing gas stream may pass horizontally through the spaces between the vertical collectorelec'trode panels whereby the particles contained in the gas, having received an ionic charge from the corona electrodes, are attracted to the panels and collect thereon.

For the most part, the panels are subjected to periodic rapping or vibration, whereupon the accumulations of solids fall toward the collecting bins mentioned earlier, especially when the cascade of solids is not broken up or carried away by the gas. Hopefully the dust agglomerates and falls in relatively large flakes. When the collector electrodes have a shape which does not conform substantially to the requirements of the system, turbulence is induced in the gases and the rapping or dust-shedding process is interfered with. Dust from the cascade is entrained by the gas and carried through the precipitator channels and must be reprecipitated at considerable cost and reduction of efficiency.

For efficient removal of the collector electrodes, moreover, the latter must be strips which are stiff and easily vibratable so that the vibrational energy applied by the rapping head is distributed throughout the collector-electrode panels without substantial damping. The problem of vibrational damping, of course, stems from the fact that a thin sheet-metal member, engaged at two edges, constitutes a membrane capable of internal deformation to the extent that such rapping energy is converted to mechanical deformation. Therefore, this energy is lost as dust-shedding energy.

To stiffen the electrodes and prevent such membranes damping of the vibrational or rapping energy, the collector electrodes are provided with a profiled configuration, i. e., are deformed to have channels, crests, corrugations or beads which stiffen the otherwise fiat central portion.

High vibratability and minimum damping of a collector-electrode strip is not, however, sufficient to insure high collecting power or efficiency because the rapping of the electrode may result in the formation of a dust cloud or agitation of the dust as noted earlier.

It has been proposed to avoid or reduce this problem by providing so-called low-flow zones in the channels traversed by the gas between the collector plates and in which the velocity of the gas drops. Such low-flow zones are able to prevent dynamic entrainment of the dust particles or to produce the necessary velocity reduction of the gas to allow sedimentation of any particles which may have been entrained. The low-flow zones may be formed by chambers produced by deformation of the sheet-metal electrodes and can constitute dust-receiving compartments to facilitate removal of the dust. The profile of the electrodes forming such chambers, of course, further stiffens the electrode strips.

Adjacent collector-electrode strips are often locked together in tight hook joints as may be made, for example, in the sheet-metal art by clamping two hook portions in interfitting relationship. They also may be joined by welding or riveting or may be connected in some other rigid manner so that the, resulting collector electrode panel is continuous in the sense that no openings are provided and the array is as stiff as possible.

A close spacing of the collector electrode panels, as described above, has the disadvantage that a strictly straight or aligned arrangement of the electrodes is impossible in practice and assembly results in bends and distortions. There is, consequently, a tendency for certain portions of the collector-electrode panels of conventional construction to be closer or further from one another and from the array of corona discharge electrodes. This not only may adversely affect gas flow but may result in undesired arcing at certain locations.

OBJECTS OF THE INVENTION It is the principal object of the present invention to provide an improved collector'electrode strip whereby the aforementioned disadvantages are obviated or reduced and a collector-electrode panel of high stability and high efficiency can be formed at relatively low cost.

It is another object of the invention to provide a collector-electrode strip extending the principles of the earlier application mentioned above and further improving on the collector electrode thereof.

Still another object of the invention is to provide a collector-electrode panel of improved construction and efficiency. Yet another object of the invention is to provide an improved electrostatic precipitator.

SUMMARY OF THE INVENTION The collector electrodes described in the aforementioned application generally are strip-shaped and are composed of sheet metal with a thickness of 1 to 1.5 mm and a hight in excess of the width of the panels which have generally flat or planar central portions and trapezoidal longitudinal-edge portions. In other words, the edge portions are unitarily and integrally deformed in trapezoidal profiles along each edge of the strip with at least one freed leg forming part of each trapezoid. The leg is formed with an outwardly bent flange or foot so that, when the collector strips are deposited in substantially contiguous relationship, side by side in a common plane, the legs of adjoining trapezoids reach toward each other and form an overlap with an air gap between them. The gap thus forms a labyrinth seal.

The longitudinal-edge portions of the collector electrodes thus define low-flow trapezoidal receiving chambers by means of which collected dust can be discharged to the bins without disturbances which might otherwise cause reentrainment of the dust with the gas stream. In short, the collector-electrode strips have a planar stiffened intermediate portion extending over the major part of the area of the strip and at the lateral edges are stiffened trapezoidally such that the outer legs of the trapezoidal stiffening profile extend below the base along of the trapezoid. The outer angle portion or foot of a pair of adjoining strips overlap one another while the major portions of the legs lie parallel to one another but are spaced apart by distances slightly greater than the width of the feet.

While the collector-electrode strip described above has been found to be highly advantageous in light of the considerations mentioned earlier, it should be noted that some disadvantages have been encountered therewith. Since the trapezoidal stiffening feet extend into the gas space along both faces of the collectorelectrode panel, some flow obstruction is created. In addition, the gaps between the adjacent strips permit some flow of air from one side to the other. This transverse flow also may be undesirable. Thus, while my prior system represents a significant improvement over the prior-art structures because of the existence of the air gap, which allows compensation of dimensional changes and permits of larger manufacturing tolerances, the slight obstruction created by the projecting legs of the trapezoids at the edges of the strips, reduces particle-collection efficiency.

It has now been found that it is possible to overcome the disadvantages of my prior system while retaining the advantages thereof by providing, instead of a generally planar central portion of the strip, flanked by narrow trapezoids, a collector-electrode strip adapted to be positioned adjacent similar strips in forming a collector-electrode panel which is subdivided into a plurality of shallow trapezoids whose broad bases open alternately on opposite sides of the strip and which are present in an odd number, preferably three.

A collector-electrode strip, according to the present invention, thus comprises three shallow trapezoids or troughs of trapezoidal profile which are geometrically congruent or similar and which are open at their broad bases while being oriented at offset between the adjacent troughs. In other words one trough opens at its broad base at one side of the strip, the adjoining troughs opens at the opposite side while the next trough opens again atthe first side. The leg of the outer trapezoids (which open toward the same side) are bent at right angles to form feet, flanges or rims at or below the plane of the broad base mentioned earlier, the latter plane simultaneously including the flattened crest formed by the narrow base of the central trapezoidalsection trough. The length of this outwardly bent leg portion is preferably less than the length of the leg so that the angle portions of a pair of adjoining electrode strips, each of which is rotated in space through a 180 with respect to the other, cover almost completely an air gap between these trapezoids located substantially along the aforementioned base planes.

The collector-electrode strips constituted in this manner have the advantage that the flattened profiles formed by the three trapezoidal troughs increase the stability of the electrode panel and enable the gas flow to hug the surfaces of the electrode with less flow separation than is the case with earlier systems. The higher stability and stiffness increases the ability of the electrode to vibrate and allows increased cleaning with low intensity rapping. Although the angled portions of the trapezoidal legs along the opposite edges of the strip almost completely cover the air gaps, the plates remain free to expand and allow assembly of the electrode panel within greater manufacturing tolerances. It has been found to be advantageous, moreover, to produce the strips by rolling on a hot-strip mill to a thickness of l to 15 mm. Furthermore, the electrode strips can be stacked or nested with facility. Shipping and storage space and costs are thereby reduced.

DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following description reference being made to the accompanying drawing in which:

FIG. 1 is an end view of an electrode strip according to the present invention;

FIG. 2 is a transverse cross-sectional view, partly in diagrammatic form, showing the relationship of two collector electrodes with other elements of an electrostatic precipitator;

FIG. 3 is a fragmentary elevational view of the lower edge of the array; and

FIG. 4 is a detailed view illustrating the junction between adjacent elements according to the present invention.

SPECIFIC DESCRIPTION In FIG. 1, I have shown the profile of a collectorelectrode strip according to the present invention. Each collector-electrode strip thus comprises three open trapezoidal section shallow channels represented at 1a, 1b and 1c, the channels being indicated generically at 1 in FIG. 2.Trapezoidal channels 1a and 1c are denominated outer channels and open codirectionally to the left in FIG. 1 while the channel lb is denominated a central or intermediate channel and opens to the right. All of the channels open in the direction of the broad base of the trapezoid.

As will also be apparent from FIG. 1, the narrow bases of the channels la 1c lie in two planes P' and P" which define the opposite faces of the electrode strip. The channels la 1c are separated by flanks 2 inclined at angles a of substantially 105(i with the narrow base or floor of the channel. The outer legs 20 are similarly inclined to the narrow base but have angled outer portions or feet 3 including angles )8 with the legs 20 wherein B 90 (i 5). In general, the length p of the foot 3 will be equal to about W w where W is the width of the broad base and w is the width of the narrow base of the trapezoid. The

legs

2 and 2a have lengths L approximately equal to W w)/[2sin (a 90)] such that the junction between the foot 3 and the leg 2a lies substantially in the plane P". The narrow bases of the trapezoidal channels are preferably formed with corrugations or parallel beads, represented generally at 10. The depth of each of the recesses 10, which likewise is of trapezoidal configuration and extends the full length of the strip, may be equal to l 1.5 mm or greater and is approximately equal to 1 to 3 times the thickness of the electrode strip. The transverse width of each of the corrugations 10 may be approximately 7 20 times the thickness t of the plate which is between 1 and 1.5 mm as indicated earlier. It has been found to be advantageous to make the troughs of such depths D as to be approximately one third to one fifth of the narrow-base width w and approximately one quarter to one sixth of the width W of the broad base. Two corrugations 10 may be provided along the narrow base of each of the trapezoidal channels.

FIG. 2 shows how the electrode strips may be positioned contiguously to form the

panels

11 and 12 defining a gas channel 13 between them. The coronadischarge electrodes 4 are disposed in a parallel array between the two electrode panels and are connected to a high voltage source 14 as represented in FIG. 2. The collector electrodes may be at ground potential. Since the subsequent strips are rotated through 180 with respect to one another, the air spaces 5 between the adjacent strips are almost completely covered by the angled portions 3, the legs 2a and the outer trapezoid portions along the plane P and P".

As will be apparent from FIG. 4, the air flow along the collector electrode strips is not obstructed and no transverse flow between the adjacent collectorelectrode strips will develop. Because the strips can be made with large tolerances, one need only arrange the angled portions 3 and the legs 2a so that the latter do not extend into the gas space and do not protrude beyond the adjacent legs. We may recess the junction between angled portion 3 and leg 2a somewhat inwardly, e. g., by 5 to 10 mm, if desired, of the associated plan P'or P".

The electrostatic precipitator, according to the present invention, also may include a fan or like means represented at 15 for inducing a flow of air between the collector electrode panels and a rapping device which may comprise a motor 16 having an eccentric hammer 17 adapted to strike an anvil l8 affixed to the upper edge of the panel. In FIG. 3, I show a fastening strip 19 to which the electrode strips 20, 21, 22 etc. are secured by bolts or rivets 23, the strips being constituted of the configuration previously described. In this case, the rapper comprises an anvil 24 at the end of the bar or strip 19, a hammer 25 and an eccentric or crank arrangement 26 of the motor 27 carrying this hammer.

I claim:

1. A collector electrode for an electrostatic precipitator comprising at least one sheet-metal strip uniformly subdivided along its width with a plurality of longitudinally extending trapezoidal cross section troughs alternately open in opposite directions along the broad bases of the trapezoid and of geometrically similar configuration, said troughs being of odd number and having depths smaller than the widths of the channels, said channels including at least two outer channels having outwardly divergent legs formed with outwardly angled portions at free extremities of said legs, the narrow bases of said channels defining respective planes along opposite surfaces of the strip, said legs lying within the region defined between said planes.

2. The electrode defined in claim 1, comprising a second electrode strip geometrically identical to the first mentioned electrode strip and rotated relatively thereto through and means securing said strips in laterally adjoining relationship with respective legs and angled portions in overlapping relationship whereby an air gap is defined between the overlapping legs and angled portions will be substantially completely covered thereby.

3. The electrode defined in claim 2 wherein each of said electrode strips is provided with three such channels.

4. The electrode defined in claim 3 wherein the narrow base of each of the trapezoidal cross-section channels is formed with a plurality of longitudinally extending corrugations.

5. The electrode defined in claim 4 wherein said electrode strips are composed of sheet-metal having a thickness of approximately 1 to 1.5 mm.

6. The electrode defined in claim 5 for an electrostatic precipitator having a second such electrode spaced from the first-mentioned electrode, said electrostatic precipitator further comprising means for inducing a flow of gas between said electrodes, an array of parallel corona-discharge electrodes disposed between the electrode strips, means for applying a high electrostatic potential across said corona electrodes and said electrode strips and means for rapping said electrode strips.

7. The electrode defined in claim 5, further comprising rapping means for jolting said electrode and a rapping bar connected to at least one of said strips.

8. The electrode defined in claim 7 wherein said bar is common to all of said strips.

Claims

2. The electrode defined in claim 1, comprising a second electrode strip geometrically identical to the first mentioned electrode strip and rotated relatively thereto through 180*, and means securing said strips in laterally adjoining relationship with respective legs and angled portions in overlapping relationship whereby an air gap is defined between the overlapping legs and angled portions will be substantially completely covered thereby.