GB2070979A

GB2070979A - Discharge electrodes for electrostatic precipitators

Info

Publication number: GB2070979A
Application number: GB8006232A
Authority: GB
Original assignee: Lodge Cottrell Ltd
Current assignee: Lodge Cottrell Ltd
Priority date: 1980-02-25
Filing date: 1980-02-25
Publication date: 1981-09-16

Abstract

A discharge electrode element for use in an electrostatic precipitator is formed from a metallic strip (1) by rolling its longitudinal edges (2) in order to form two strip electrodes, one at each end of a connecting web (4). The strip electrodes each comprise at least two portions extending in opposite directions, as shown three portions (3, 5, 6), and are arranged in planes substantially normal to the plane of the web. The adjacent rolled-over portions of the edges (2) are in close proximity to one another. The edges (7) of the strip electrodes may be serrated into order to improve the corona discharge effect, and the web (4) may be provided with a longitudinal strengthening rib (8). Various embodiments are described with reference to other Figs. <IMAGE>

Description

SPECIFICATION Discharge electrodes for electrostatic precipitators This invention relates to electrostatic precipitators and in particular to discharge electrodes therefor, and methods of manufacturing them.

For the cleaning of, for example, dust-laden gases either single stage of double stage electrostatic precipitators may be employed.

In a single stage precipitator large area collector electrodes all generally connected to ground are arranged in parallel rows and pluralities of rod, wire or narrow plate discharge electrodes are positioned between the collector electrodes. In double stage precipitators the discharge electrodes are positioned in a row normal to the rows of collector electrodes and spaced apart from the collector electrodes at the gas inlet side thereof, the discharge electrodes being alternated with grounded receiving electrodes, and alternate collector electrodes being grounded.

During operation of single stage precipitators the discharge electrodes, as well as the collector electrodes, soon become covered with a layer of dust which is detrimental to the corona effect. In order to overcome this the discharge electrodes are rapped in a similar manner to the collector electrodes, whereby to make the dust fall off and into dust collection hoppers. The design of the discharge electrodes must therefore be such that they can withstand the rapping operation.

Various forms of suitable discharge electrodes have already been proposed which employ long thin piates that can be mounted between uper and lower frames in order to provide rigidity and facilitate rapping of a plurality of electrodes simultaneously.

One known form of discharge electrode is disclosed in British Patent specification No.

998,268 and employs metal strips to the lateral eges of which are rolled in or bent out and are provided at intervals with pressed out parts or projections which act as discharge points. British Patent specification No.

931,495 discloses a discharge electrode formed from an essentially flat plate by bending the two lateral edges to form two stiffening borders which are in a plane essentially normal to the plane of the plate, discharge spikes being punched out of the plate material along these stiffening borders and bent substantially normally to the plane of the plate.

From British Patent specification No.1,145,770 is known a discharge electrode which is bent from a plate such as to provide ridges of trapezoidal cross-section which project on alternate sides of the electrode. Corona discharge points are arranged on these faces of the ridges which are parallel to the main plane of the plate and project away from the electrode. In another known arrangement, as disclosed in British Patent specification No.

888,871, pairs of strip discharge electrodes with smooth or toothed edges are united by a stiffening member which may comprise a sheet metal plate, the strip electrodes extending in planes substantially normal to the plane of the sheet metal stiffening plate. In a further known arrangement, as disclosed in British Patent specification No. 855,621, a strip discharge electrode is formed from a plane or angular sectioned strip such as right-angled, T or double-T, discharge points being formed by bending incised points out from the plane strip.

It is an object of the present invention to provide an alternative form of discharge electrode member for use in an electrostatic precipitator and a method of manufacturing such an electrode.

According to one aspect of the present invention there is provided a one-piece electrostatic precipitator discharge electrode member comprising a metallic strip whose longitudinal edges each form a respective strip electrode, which strip electrodes lie in planes substantially normal to the plane of a web of the metallic strip connecting the strip electrodes, first portions of the edges adjacent the web extending substantially normally to the web in respective first directions away from the web and second portions of the edges adjacent the first portions extending in respective second directions opposite to the respective first directions, the first and second edge portions being in close proximity to one another.

According to another aspect of the present invention there is provided an electrostatic precipitator comprising a casing, a plurality of collector electrodes mounted in the casing and a plurality of discharge electrode members mounted in the casing between adjacent pairs of collector electrodes and each comprising such a one-piece discharge electrode member.

According to a further aspect of the present invention there is provided a flat blank for use in providing such a one-piece discharge electrode member and comprising first and second longitudinal edge portions, in each of which are punched rows of apertures along two parallel axes, and an intermediate web.

According to yet another aspect of the present invention there is provided a method of manufacturing a discharge electrode comprising the steps of providing such a flat blank and deforming the blank by rolling such that two strip electrodes are formed with rows of apertures along their longitudinal edges.

According to yet a further aspect of the present invention there is provided a discharge electrode member manufactured by such a method.

According to still another aspect of the present invention there is provided a method of making a one-piece electrostatic precipitator discharge electrode member comprising rolling the longitudinal edges of a metalilic strip whereby to form strip electrodes extending in planes substantially normal to the plane of the remainder of the strip, which provides a web joining the strip electrodes, first portions of the edges adjacent the web extending in a first direction away from one side of the web, second portions of the edges adjacent the first portions extending in a second direction opposite to the first direction to the plane of the web, third portions of the edges adjacent the second portions extending in the second direction on the other side of the web, and fourth portions of the edges extending in the first direction towards the web, the first and second, and third and fourth portions, being in close proximity to one another.

Embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a cross-section through one form of rolled two strip discharge electrode member; Figure 2 shows a cross-section through a variant form based on the rolled two strip discharge electrode member of Fig. 1; Figure 3 shows a cross-section through a further variant form based on the embodiment of Fig. 1; Figure 4 shows a cross-section based on the embodiment of Fig. 3 and including a stiffening portion; Figure 5 shows a cross-section through a four strip discharge electrode member based on the embodiment of Fig. 4; Figure 6 shows a part of a punched metal plate prior to rolling; Figure 7 shows an end view as seen in direction A indicated in Fig. 4, of a strip electrode rolled from a punched plate as shown in Fig. 6;; Figure 8 shows a portion of a rolled strip electrode, as seen in the direction B of Fig. 4, in which apertures are punched in the plate between the two strip electrodes; Figure 9 shows schematically, a side view of a single stage precipitator employing discharge electrode members manufactured according to the present invention, and Figure 10 shows, schematically, a partial plan view of the precipitator of Fig. 9 indicating the relative positioning of the collector and discharge electrodes.

The present invention employs a rolling process to form two, or more, strip discharge electrodes from a single plate of metal.

One basic form of discharge electrode member is Selc,wr) in cross-section Fiy. 1 It is formed frorn a metal plate or strip 1 whose lateral edges 2 are rolled such as to provide first sections 3 extending substantially normally to the plane of a central portion or web 4 in one direction away from the central portion 4, and second sections 5 also substantially normal to the plane of the central portion 4 but extending in the opposite direction, the second sections extending at least back to the plane of the central portion 4. In the embodiment of Fig. 1, the second portions 5 extend further than the central portion.

The adjacent portions of the first sections 3 and the second sections 5 are in close proximity to one another. Each of the rolled lateral edges 2 of the plate 1 functions as a separate discharge electrode, the central portion or web 4 serves to connect them together.

Fig. 2 shows a modification of the basic form of Fig. 1, in that one lateral edge 2' is bent away from the central portion 4 in the opposite direction to the other lateral edge 2".

The efficiency of the electrodes of Figs. 1 and 2 may be improved by rolling the outermost part 6 of the second portions 5 back on themselves as shown for example, in Fig, 3.

Alternatively parts 6 could be rolled onto the outermost side of portions 5. The corona discharge tends to be concentrated at the curved edges 7 of the discharge electrodes, whereas there is a non-corona field generated at the central portion 4.

In order to improve the rigidity of the discharge electrode member the central portion 4 may be deformed as shown in Fig. 4, to effectiveiy provide a strengthening rib 8.

More than one such rib may be provided if desired. The rolled edges 2 of the electrode member also act to improve the rigidity.

Whilst the electrode members described above comprise two electrode strips which are joined together, it is alternately possible to join three, four or more electrode strips together in a similar manner by suitably rolling a plate of the necessary width. The electrode member shown in Fig. 5 has two electrode strips 9, two electrode strips 9' and three strengthening ribs 10 but is formed from a single plate or strip of metal. The two electrode strips 9' are serpentine in cross-section with their adjacent portions in close proximity with one another.

Various means may be employed to improve the corona discharge and thus the efficiency of a precipitator employing the discharge electrode members of the present invention.

If the lateral edges 2 of the plate are punched with for example, elongate apertures 11 (Fig. 6) at spaced positions along the bending axes 1 2 before the plate is rolled, the rounded smooth edges 7 of the above described electrodes will be replaced by serrated edges 13, as shown in Fig. 7, when the plate has been rolled. These serrations 1 3 will substantially increase the corona discharge by providing additional edges for concentration of the electrical charge. In a modification the apertues 11 are of other shapes e.g. circular.

Whereas the non-corona field at the central portion 4 of the electrodes is believed to improve the efficiency of precipitation, the extent of the corona dicharge itself can be increased by punching circular holes 14 in the central portion 4 adjacent to the bent lateral edges 2, as shown in Fig. 8, which circular holes will provide sharp discharge points. In a modification the holes 14 are non-circular. In another modification the circular or non-circular holes 1 4 extend over the whole of the central portion 4 and not just adjacent the edges 2.

An electrostatic precipitator including discharge electrode members of the present invention is shown somewhat schematically in Figs. 9 and 10. It comprises a casing 15, a plurality of spaced collector electrodes 1 6 (only one of which is visible in Fig. 9) independently supported in the casing 1 5 and a plurality of 2 strip discharge electrode members 1 7 supported in the spaces between the collector electrodes 1 6 (see Fig. 10). The electrodes 1 7 in a particular row are mounted between a respective top frame 1 8 and a bottom frame 1 9 and are suspended from the roof 20 of the casing, as are the collector electrodes.Conventional rapping gear (not shown) may be located on the roof of the casing and effective on the collector and discharge electrode support frames. Dust laden gas passes into the casing 1 5 through an inlet 21 in the direction X and the cleaned gas passes out of the casing through an outlet 22.

Precipitated dust rapped from the collector and discharge electrodes leaves the casing via an outlet 23. The precipitator also comprises means (not shown) for supplying high potentiat to the discharge electrode members 17, the collector electrodes being connected to earth.

The one-piece rolled discharge electrode members provided by the present invention have, in comparison with a conventional mast electrode design, simpler manufacture, improved rigidity, better transmission of rapping efforts and stronger resistance to top and bottom frame swing. Tests have shown that an acceptable corona discharge can be ob tamed with such a one-piece rolled electrode (serrated) at aproximately 50% of the discharge current from a similar sized two wire mast electrode, with the resultant advantage of a reduced power consumption in the precipitator, since a lower current is dissipated for the same voltage. This is apparently derived from the non-corona element of the electrical discharge. Both the smooth edge and serrated edge versions of the electrode members described above are considered to have sufficient corona and non-corona discharge to obtain an acceptable dust precipitation efficiency.

Claims

1. A one-piece electrostatic precipitator discharge electrode member comprising a metallic strip whose longitudinal edges each form a respective strip electrode, which strip electrodes lie in planes substantially normal to the plane of a web of the metallic strip connecting the strip electrodes, first portions of the edges adjacent the web extending sustantially normally to the web in respective first directions away from the web and second portions of the edges adjacent the first portions extending in respective second directions opposite to the respective first directions, the first and second edge portions being in close proximity to one another.

2. An electrode member as claimed in claim 1 and including third portions of the edges adjacent the second portions, which third portions extend in the respective second directions and away from the web on the opposite side of the web to the first and second portions.

3. An electrode member as claimed in claim 2 and including fourth portions of the edges adjacent the third portions, which fourth portions extend in the respective first directions towards the web, the third and fourth portions being in close proximity to one another.

4. An electrode member as claimed in claim 3, wherein the fourth portion of each strip electrode is in the same plane as the respective first portion.

5. An electrode member as claimed in any one of the preceding claims wherein the first portions extend in the same first direction away from the web.

6. An electrode member as claimed in any one of the preceding claims, wherein the web includes one or more additional strip electrodes intermediate the said strip electrodes, the or each additional electrode being serpentine in cross-section with adjacent portions thereof in close proximity to one another.

7. An electrode member as claimed in any one of the preceding claims wherein the or each web between the strip electrodes is or are, respectively, deformed to provide a longitudinal strengthening rib.

8. An electrode member as claimed in any one of the preceding claims, wherein longitudinal edges of the strip electrodes are provided with corona discharge improving apertures.

9. An electrode member as claimed in claim 8 wherein the or each web is provided with corona discharge improving apertures.

10. A one-piece electrostatic precipitator discharge electrode member substantially as herein described with reference to and as illustrated in Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig.

5, Figs. 6 and 7, or Fig. 8 of the accompanying drawings.

11. An electrostatic precipitator comprising a casing, a plurality of collector electrodes mounted in the casing and a plurality of discharge electrode members mounted in the casing between adjacent pairs of collector electrodes and each comprising a discharge electrode member as claimed in any one of the preceding claims.

12. An electrostatic precipitator as claimed in claim 11 and substantially as herein descnbed with reference to Figs. 9 and 10 of the accompanying drawings.

1 3. A flat blank for use in producing a discharge electrode member as claimed in claim 8 and comprising first and second longitudinal edge portions, in each of which are punched rows of apertures along two parallel axes, and an intermediate web

1 4. A method of manufacturing a discharge electrode member comprising the steps of providing a flat blank as claimed in claim 1 3 and deforming the blank by rolling such that two strip electrodes are formed with their longitudinal edges coinciding with the parallel axes.

1 5 A discharge electrode member manufactured by a method as claimed in claim 14.

1 6 A method of making a one-piece electrostatic precipitator discharge electrode member comprising rolling the longitudinal edges of a metallic strip whereby to form strip electrodes extending in planes substantially normal to the plane of the remainder of the strip, which provides a web joining the strip electrodes, first portions of the edges adjacent the web extending in a first direction away from one side of the web. second portions of the edges adjacent the first portions extending in a second direction opposite to the first direction to the plane of the web. third portions of the edges adjacent the second portions extending in the second direction on the other side of the web, and fourth portions of the edges extending in the first direction towards the web, the first and second, and third and fourth portions. being in close proximity to one another.

17. A method as claimed in claim 16, further comprising rolling a longitudinal strengthening rib into the web.

18. A method as claimed in claim 1 6.

further comprising rolling the web to provide one or more additional strip electrodes which are serpentine in cross-section with adjacent portions in close proximity to one another.