US2589463A - Electrostatic precipitator - Google Patents

Description

March 18, 1952 ELECTROSTATIC PRECIPIT Filed May 51, 1950 l" s a R. W. WARBURTON ATOR Patented Mar. 1.8, 1952 ELECTROSTATIC PRECIPITATOR Ray W. Warburton, Medield, Mass., assigner to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Bennsylvania Application May 31, 1950, Serial No. 165,287

1 Claim.

This invention relates to electrostatic precipitators for removing small foreign particles such as dust, from* gases such as air.

The most commonly used electrostatic precipitators for cleaning air, employ closely spaced, metal, collector plates between which electrostatic elds are maintained, and on which `the dust and other foreign particles are deposited. When the plates have become loaded with deposited matter, it has been the practice to wash them down with water or other ushing liquids. In many locations, however, the collected foreign matter becomes so bonded to the plates through mechanical and chemical action that it is-diicult if not impossible to remove it by washing. The plates then have to be disassembled and scraped or replaced, since their continued use .without cleaning would result in arc-overs and probable damage to the associated power supply apparatus.

While in industrial plants and other places where experienced servicemen are readily available for servicing electrostatic precipitators, the cleaning of the collector plates while troublesome, has been accepted as necessary, and has not interfered with theirV use since their advantages greatly outweigh their disadvantages.

However, the situation is different where electrostatic precipitators are used in homes. In some cases it is impractical or inconvenient to provide facilities for washing the collector plates, and even where such facilities are provided and properly used, their action is sometimes not sulficient, as described in the foregoing, to adequately clean the collector plates. This usually results in the calling in of an outside serviceman, or in disuse of the equipment.

In my co-pending applications, Serial Nos. 62,931 filed August 24, 1948, now Patent 2,571,079 dated October 9, 1951, and 73,277 filed January 23, 1949, now latent 2,579,445 dated December i8, lsl, I have disclosed different forms of collector cells for electrostatic precipitators Which are so inexpensive and easily handled that it is practical and economical'to remove them and to replace them with new ones, when they have become loaded with collected matter. Such cells comprise intermeshed filaments having i'elatively high electrical resistances. Electrical currents iiowing through the filaments produce voltage drops therethrough and which establish electrostatic fields therebetween which are suiiicient to cause electrostatically charged dust particles to be deposited thereon. The principle involved is given in the following.

If a difference in potential is applied to the opposite ends of an electrical conductor, then current will iiow through the conductor. If .the voltage at one end of the conductor is lZKV and that at the other end of the conductor is 0, and the power supply source has sufiicient capacity to handle the load without voltage attenuation, then regardless of the resistance of the conductor, assuming uniform resistance along its length, the midpoint of the conductor will be ata, GKV potential, a point midway between its center and its high voltage vend will have a potential of SBKV, and a point midway between its center and its zero voltage end willhave a vpotential of SKV. According to Ohms law, a low resistance conductor `will draw large currents and a high resistance conductor will draw small currents.

In the collector cell disclosed in this and in said applications, the resistance of the intermeshed filaments is so high that the total current drawn from an associated power pack is in the order of milli-amperes.

The collector cell of the present application differs fromv those of said pending applications through using grounded wire screens at the inlet and outlet of the cell for retainingA the intermeshed filaments in place, andl for grounding the outermost filaments, and in using a central wire screen for charging centrally located filaments.

It has been proposed heretofore to establish electrostatic fields between adjacent intermeshed filaments in a Vcollector cell, but the filaments of such a cell were dielectric's so that the voltages thereon provided by opposite charges applied at spaced points, were produced by polarization. The electrostatically charged dust particles on depositing upon such non-conducting filaments provided an accumulative space charge, opposing further collection, since the charges could not leak off to ground. With current flow through the filaments as occurs in the cells of this and of said applications, the electrostatic charges do leak off to ground as fast as the electrostatieally charged particles are collected, so that no space charge can exist.

An object of this invention is to provide an inexpensive, disposable, `collector cell for an electrostatic precipitator.

Another object of this invention is to provide a disposable collector cell for an electrostatic precipitator which can easily be removed from and replaced in, the precipitator.

The invention will now be described with reference to the drawing, of which:

Fig. `1 is a, transverse section through a co1- lterminal of a power pack.

3 lector cell embodying this'invention, the section being taken along the lines I-I of Fig. 2

Fig. 2 is a plan view looking downwardly upon the cell;

Fig. 3 is a sectional view along the lines 3-3v of Fig. 2;

Fig. 4 is a side elevation, in section, of an electrostaticprecipitator including the cell of Figs. 1-3;

Fig. 5 is a circuit diagram for explaining the principle of operation of the invention, and

Fig. 6 is a partial transverse sectional View of the cell showing a charged wire centrally located between four grounded wires.

Referring first to Fig. 5 of the drawing, the upper filament I is connected to the -l-I2KV It is connected at one end through the resistor II to one end of an adjacent parallel filament I2, and at its other end through the resistor I3 to the other end of the filament I2. The filament I2 is also connected at its said one end through the resistor I4 to one end of an adjacent parallel filament I5, and at'its other end through the resistor I6 to the other end of the filament I5. The lament I is also connected at its said one end through the resistor I'I to one end of the adjacent parallel filament I8, and at its other end through the resistor I94 to the other end of the filament I8. The filament I8 is also connected at its said one end through the resistor 20 to one end of the adja# cent parallel filament 2|, and at its other end through the resistor 22 to the other end of the filament 2l. 'I'he filament 2! is grounded and connected to the negative or zero voltage terminal of the power pack.

Assuming that the resistors all have the same value and that the filaments have relatively low resistance so that the voltage drop through them is of no consequence, then the current flow through the filaments and resistors will cause the filament I2 to have a 9KV potential, the filament 6 to have a SKV potential, and the lament I 8 to have a 3KV potential, there thus being a SKV difference in potential between adjacent filaments.

If other filaments were placed between the iilaments I0 and I2 and connected at their ends to the resistors II and I3, they would take on potentials between the values -l- I 2KV and -j-SKV. The voltages between adjacent filaments would then be less, but so would the intervening distances, so that the electrical field Awhich varies directly as the voltage and inversely as the spacing, would be the same as if the laments were spaced further apart.

In a cell embodying this invention, the same principleof operation is involved, but the action is more complex since the filaments I I), I2, I5, I8 and 2l would be resistors. There would be current flow through, and voltage drops in, the filaments I0, l2, I5, I8 and 2|. But adjacent filaments would have different potentials thereon so that electric fields would exist therebetween. This may be understood with reference to Fig. 6 of the drawing where rcurrent flows between a Icentral wire 38 and each of the outer wires 33 and 34, through the iilaments 36 which contact each other and the wires. Between the central wire and each outer wire there are a plurality of filaments electrically connected in series-parallel, the current flow through the filaments producing voltage drops therein. i

Referring now to Figs. 1 to 3 of the drawing,` the metal casing 30 has an open inlet side 3I and an open outlet side 32. The small, metal wires 33 extend crosswise the inlet of the casing in spaced parallel relationship, being grounded in the casing at their ends. The similar wires 34 extend crosswise the outlet of the casing in spaced parallel relationship, being also grounded to the casing at their ends, corresponding wires 33 and 34 being in alignment.

The intermeshed filaments 36 are packed in between the wires 33 and 34 and contact same and the sides of the casing. The filaments are of relatively high resistance conducting material, such as threads of urea plastics, glass wool coated with petroleum jelly, or asbestos fibres.

A metal screen consisting of the end wires 3l extending at right angles to the wires 33 and 34, and of the wires 3B, extending parallel to the wires 33 and 34, is inserted within the mesh of filaments with the wiresy 38 midway between the wires 33 and 34 but staggered with respect thereto, so that the axes of the wires 38 are positioned in planes midway between planes in which the axes of adjacent wires 33 and of adjacent corresponding wires 34 occur.

tween which are the ionizer wires 44'supportedl from the electric insulators 45. The wires 44 are adapted to be connected to the -j-I3KV terminal of a conventional, high voltage, power pack, and the casing 42 with the tubes 43 are adapted to be connected to the grounded negative terminal of the power pack. The construction described so far in connection with Fig. 4 is conventional.

A cell such as is illustrated by Figs. 1-3 of the drawing is slid into the casing 42 through its gas outlet 4B so that it is located downstream of the ionizer electrodes 43 and 44. The wire 40 f is connected to the +I3KV terminal of the power pack. The casing of the cell is grounded to the casing 42.

In operation, the air passing between the,

ionizer electrodes 43 and 44 is ionized causing ...1, dust particles entrained in the air to be given positive electrostatic charges. The charged dust then deposits upon the filaments 33 in the collector cell 3U.

In the cell 33, since the central wires 38 are at a +i3KV potential, and the grounded outer wires 33 and 34 are at Zero potential, and since the central wires and the outer wires are electrically connected by the high resistance filaments 36 therebetween and in contact therewith, electric current flows through the filaments between each central wire 38 and adjacent outer wires 33 and 34, this current iiow providing voltage drops through the filaments and establishing diierent electric potentials in different laments. The

' filaments closest to the wires 38 would have higher Y voltages thereon, while those closest to the wires 33 and 34 would have lower voltages thereon, the other laments having voltages thereon dependent upon their relative positions.

Thus, adjacent filaments have different poten tials thereon so that electrostatic elds existtherebetween. Although these fields have low intensity, since the spacing between adjacent points is small, the fields are sufficient to cause 'l'electrostatieally charged dust particles to be deposited thereon. Laboratory tests have shown that electrostatically charged dust particles are collected much more effectively when voltage from the power pack is applied to the cell 39 than when the voltage is removed. Also, that smoke such as tobacco smoke and smoke from a smoke bomb will pass freely through the cell when the voltage is removed therefrom, but is completely removed when the voltage is applied.

When the cell becomes loaded with dust, it can be slidaoly removed through the outlet 45 or" the casing Ps2 and replaced with a clean one. The loaded cell can be then discarded since its cost is low.

While one embodiment of the invention has been described for the purpose of illustration, it should be understood that the invention is not limited to the exact apparatus and arrangement cf apparatus illustrated, since modifications thereof may be suggested by those skilled in the art without departure from the essence ofA the invention.

What I claim as my invention is:

A collector cell for an electrostatic precipitator comprising a frame defining a gas passage having open ends, a first plurality of spaced apart wires having parallel axes extending substantially in a common plane across one of said ends, a second plurality of spaced apart wires having parallel axes extending substantially in a common plane across the other of said ends, a third plurality of spaced apart wires having parallel axes extending substantially in a common plane across said passage midway between the planes of said first and second pluralities, said planes being substantially parallel to each other, said wires having relatively low electrical resistances, and intermeshed electrically conductive filaments having relatively high electrical resistances lling the space between the wires of said rst and third pluralities, and the space between the wires of said second and third pluralities, and means for applying a direct current electrical potential to the wires of said third plurality, and for applying a direct current potential having the opposite polarity to said rst mentioned potential to the wires of said first and second pluralities.

RAY W. WARBURTON.

REFERENCES CITED The following references are of record in the le o this patent:

UNITED STATES PATENTS Number Name Date 2,297,601 Williams Sept. 29, 1942 FQREIGN PATENTS Number Country Date 96,717 Sweden July 6, 1939

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