US2925882A - Electrostatic precipitators - Google Patents

Description

Feb. 23, 1960 w. BosTocK 2,925,882

ELECTROSTATIC PRECIPITATORS I Filed April 30, 1958 4 Sheets-Sheet 1 Feb, 23, 1960 w. BOSTOCK 2,925,882

ELECTROSTATIC PRECIPITATORS Filed April 30, 1958 4 Sheets-Sheet 2 u 1 I *E E Q E a I I I 'l -!i H [M 1m Ill WE n :l I! :1 n :3

Feb. 23, 1960 w. BOSTOCK ELECTROSTATIC PRECIPITATORS 4 Sheets-Sheet 3 Filed April 30, 1958 Mh/ k Feb. 23, 1960 w. BOSTQCK 2,925,882

ELECTROSTATIC PRECIPITATORS Filed April 50, 1958 4 Sheets-Sheet 4 signor to Simon-Carves Limited, Stockport, Cheshire, England, a company of Great Britain Application April 30, 1958, Serial No. 732,065

6 Claims. (Cl. 183-7) This invention has for its object to provide an improved construction of electrostatic precipitator in which the removal of precipitated dust from the collecting electrodes is facilitated.

This application is a continuation-in-part of my copending application Serial No. 589,401, filed June 5, 1956, now abandoned.

According to the invention, each collecting electrode comprises movable sections with surfaces disposed alternately in regions of high and low H.T. current density, and means are provided for periodically displacing said sections to move thesurfaces in regions of high current density to regions of low current density and vice versa.

In a convenient embodiment of the invention, each collecting electrode is made up of a number of sections arranged in planes parallel to the gas flow, with strips located between adjacent sections arranged at right angles to the gas flow, the said sections being arranged in staggered relationship so that alternate sections are in line with opposite edges of the intervening strips and means are provided for displacing the said sections at intervals in directions at right angles to the gas flow, so as to bring each into line with the opposite edges of the adjacent strips, discharge electrodes being provided opposite the said sections and on both sides thereof.

. With this arrangement the collecting surface on each side of the electrode consists in effect of a number of spaced channels, the base of a channel being one of the said sections and the sides being the strips adjacent thereto, the channels being separated by alternate sections. It is found that under corona discharge conditions high tension current from a discharge electrode facing a channel flows almost entirely to the strips forming the sides of the channel, the flow to the section forming the base of a channel being negligible. Conditions are therefore favourable for dislodging dust previously collected on this section, as even dusts which are normally difiicult to remove from the electrodes are readily dislodged when no current is flowing. The other side of such a section of course forms a space between two channels facing the ql ischarge electrodes on the other side of the collecting electrode, and it receives the full flow of current from thehlischarge electrode facing it, and therefore collects dust.

After a suitable period, before the dust deposits can seriously affect the precipitator performance, all the electrode sections are displaced, so that the surfaces which have collected dust move away from their associated discharge electrodes and take up positions in which they form the bases of channels to which only a very small current flows. The dust collected then loses its electric charge almost completely and can readily be dislodged by the standard cleaning techniques, e.g. rapping. As the sections move they dislodge dust which has collected on the strips forming the sides of the channels, thereby maintaining them in a reasonably clean condition.

The dust is thus dislodged under the most favourable conditions, i.e. when only a small current is flowing, but

2,925,882 Patented Feb. 23, 1960 ice without having to interrupt the operation of the precipitator by temporarily cutting off the current supply, and the electrodes are always maintained in a sufiiciently clean state so as not to interfere with the collecting eificiency of the system.

The electrode sections may be suspended from a shaft which is turned at intervals in opposite directions. Alternate sections may be carried by lugs beneath the shaft and by hoops or the like on lugs above the shaft, so that alternate sections move in opposite directions. The vibration caused by displacement may be sufiicient to dislodge the dust, or rapping gear may be provided for rapping the sections after they have been displaced.

Referring to the accompanying drawings:

Figure 1 is a sectional plan view of one of the through ducts of an electrostatic precipitator fitted with collecting electrodes according to the invention.

Figure 2 is a sectional view on the line II--II of Figure 1.

Figure 3 is a sectional view on the line III-III of Figure 1.

Figure 4 is a sectional plan view of an electrostatic path which the discharge current takes to the collecting electrodes.

Figure 5 shows a part ofthe precipitator of Figure 4 with the electrode sections in different positions and showing the changeover of'the discharge current field pattern.

Referring to Figures l-3, each collecting electrode consists of a number of sections, 1 and 2, arranged in staggered relationship in planes parallel to the gas flow, and strips 3 located between adjacent sections and arranged at right angles to the gas flow. The sections are in line with the rear edges of strips 3 and the sections 2 are in line with the front edges. An H.T. frame 4 carries the discharge electrodes 5, being supported outside the duct in a known manner.

The strips 3 are connected to form a rigid framework by plates 6 and 7 and angles 8. Passing through the top of this frame is a shaft 9, to which are rigidly attached brackets or lugs 10 and 11 for supporting the sections 1. The brackets 10- support the sections 2 directly as shown and the brackets 11 support the sections 1 on the opposite side of the strips 3, through hoops 12. By rotating the shaft 9 through a small angle in the appropriate directions, the sections 1 and 2 are transposed to the positions 1a, 2a respectively. Positions of high currentdensity now become positions of very low current density and vice versa.

At the tops of sections 1 are attached angle brackets 13, which carry sheets 14 of sutficient length and width to cover the spaces between the strips 3. These serve the dual purpose of closing the tops of the spaces between the strips 3 to the passage of dust-laden gas and of preventing the sections 1, 2 from falling into the precipitator duct where they may fall against the H.T. framework and cause a short in the H.T. circuit. The top of the duct, between the collecting electrodes, is closed to the passage of dust-laden gas by sheets 15 and the whole of the operating mechanism is contained in a comparatively dust-free space. The lower ends of the sections 1 and 2, lead directly into a standard collection hopper (not shown).

The mode of operation is as follows. Dust collects at the positions of high current density, as shown by the shaded portions 16 in Figure 1. After a suitable period, all the electrode sections 1 and 2 are displaced by turning the shafts 9, so that the surfaces which have collected dust move away from their associated discharge electrodes and take up positions in which they form the bases of channels to which only a very small current is flowing. As the sections move the first potential loosening takes place when the dust layer is broken. This is followed by a scraping action of the sections 1, 2 on the dust which has collected on the strips 3 forming the sides of the channels, thereby maintaining them in a reasonably clean condition, when the sections reach the position of base of a channel, the collected dust loses its electric charge and can readily be dislodged by the standard cleaning techniques, e.g. rapping.

The movement of shaft 9 for transposing the sections can be obtained by means of a suitably shaped cam or similar reciprocating device. The vibration caused by the displacement may be sufiicient to dislodge the dust without the necessity of using rapping mechanisms.

Figures 4 and 5 show an electrostatic precipitator according to the invention, it being understood that conventionally a number of precipitators are usually installed both behind and beside each other.

Each precipitator comprises end walls 21 and 22, an open inlet zone 23 and an open outlet zone 24.

The working parts of the precipitator comprise fixed collecting electrode sections 25, 26 and 27 and movable collecting electrode sections 28, 29 and 30.

The fixed collecting electrode sections 25 are located in a row next to the containing wall 21, the fixed col lecting electrode section 26 in a row next to the containing wall 22 and the fixed collecting electrode sections 27 in intermediate rows. All these electrode sections are at right angles to the direction of flow of the dust-laden gases.

The movable collecting electrode sections 28 are located next to the containing wall 21 between fixed sections 25 and the movable collecting electrode sections 29 next to the containing Wall 22 between fixed sections 26. Movable collecting electrode sections 30 are mounted between the fixed sections 27. All these electrode sections are parallel to the direction of flow of the dust-laden gases.

Discharge electrode frames 31 are held in a known manner between the rows of collecting electrode sections and each carries a number of discharge electrodes 32. The frames 31 are electrically connected to H.T. busbars 33.

The movable electrode sections are supported as shown in Figures 2 and 3 and are displaced at predetermined time intervals with respect to the fixed electrode sections, their extreme positions being illustrated in Figures 4 and 5 respectively.

From this can be gathered that the movable electrode sections 25, 26 along the two containing walls 21 and 22 are alternately in a region of high current density and in a region of low current density on one face only whilst all other movable electrode sections have one face in a region of high current density, and the other opposite face in a region of low current density, these positions being interchangeable. The fixed collecting electrode sections 25, 26 near the containing walls 21 and 22, and those sections 27 which are at the ends of their respective rows, have one face in a region of high cur- 4 rent density while the other is shielded from the discharge current, the positions being reversed. All other fixed collecting electrodes have both faces continuously exposed in regions of high current density. Dust collects at the positions of high current density, as shown at 34 in Figure 4.

WhatI claim is:

1. An electrostatic precipitator comprising collecting electrodes each made up of a number of sections arranged in planes parallel to the gas flow, with strips located between adjacent sections arranged at right angles to the gas flow, the said sections being arranged in staggered relationship, so that alternate sections are in line with opposite edges of the intervening strips, means for displacing the said sections at intervals in directions at right angles to the gas fiow, so as to bring each into line with the opposite edges of the adjacent strips, and discharge electrodes opposite-the said sections.

2. An electrostatic precipitator as claimed in claim 1,

and having a shaft, means for turning the shaft at intervals in opposite directions, means extending downwards from the shaft for suspending alternate collecting electrode sections, and means extending upwards from the shafts for suspending the intervening collecting electrode sections, whereby adjacent sections are moved in opposite directions as the shaft is turned.

3. An electrostatic precipitator comprising a first group of fixed collecting electrodes positioned at right angles to the gas flow, a second group of movable collecting electrodes positioned parallel to the gas flow and arranged for movement relative to thefixed collecting electrodes, and means for moving the collecting electrodes of the second group periodically from regions of high current density to regions of low current density and vice versa while at least the major portion of the collecting electrodes of the first group remain in regions of high current density.

4. An electrostatic precipitator as claimed in claim 3, in which discharge electrodes are provided opposite the movable electrodes and on both sides thereof.

5. An electrostatic precipitator as claimed in claim 3, in which the displacement of the movable electrodes is at right angles to the gas flow.

6. An electrostatic precipitator as claimed in claim 3,

, having a shaft, means for turning the shaft at intervals in opposite directions, means extending-downwards from the shaft for suspending alternate movable electrodes and means extending upwards from the shaft for suspending the intervening movable electrodes, whereby adjacent electrodes are moved in opposite directions as the shaft is turned.

References Cited in the file of this patent UNITED STATES PATENTS Sweden Ian. 1.3, 1953'

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