US2181767A - Electrostatic precipitator - Google Patents

Description

G. w. PENNEY 2,181,767

ELECTROSTATIC PREGIPITATOR Nov. 28, 1939.

Filed May 6, 1938 INVENTOR aW/ eme i ATTORNEY Patented Nov. 28, 1939 UNITED STATES PATENT OFFICE ELECTROSTATIC PRECIPITATOR of Pennsylvania Application May 6, 1938, Serial No. 206,381

3 Claims.

My invention relates to electrical precipitators for atmospheric dust, and particularly, although not necessarily, such precipitators as may be used for the conditioning of air which is to be breathed.

The present invention is an improvement over that which constitutes the subject matter of my application Serial No. 45,070, filed October 15, 1935, Patent No. 2,129,783, granted September 13, 1938, relating to a gas-purifying precipitator in which the gas is blown first through an ionizing chamber, and then through a separate precipitating chamber, a significant feature of the precipitator being that the ionizing wire is of such small diameter, or so small in proportion to its distance from its associated grounded electrodes, that practically utilizable ionization of suspended particles in the gas may be obtained at a wirecharging voltage which is below the critical corona voltage, so that the wire-charging voltage may be below this critical value, thereby limiting the ionizing current input and also limiting the ozone-generation when the precipitator is used for cleaning air.

Such a precipitator utilizes an ionizing wire having a diameter of less than one-fortieth of the distance from the wire to the nearest grounded electrode, or less than 32 mils thickness, which thickness is a somewhat roughly critical value of the wire-diameter, somewhere near the knee of the curve expressing the relation between the critical corona voltage and the wire diameter. In ordinary practice, the wire is much finer than this upper limit, and is frequently a tungsten wire 5 mils in diameter, or even very much less in diameter. In order to ensure against breakage and to facilitate handling of the equipment, the endsupports for such a fine wire must be fairly rigid and strong, and if the wire is longer than about a foot, it should be supported at frequent inter- 40 vals along its length, say at every 8 inches, in order to protect it against vibration and breakage, or, in remote cases, against excessive sagging. These supports introduce dark spots along the wire, extending for some half inch to three-quarters of an inch on either side of the support, defining regions at which the ionizing current is quite inadequate, so that the air or gas which passes these regions is not adequately ionized, thus reducing the efliciency of the precipitation. It is an object of my invention to avoid the foregoing difliculties.

According to my present invention, I provide additional ionizing means at the wire-supporting points, such means preferably comprising suitably selected pronged means comprising prongs extending out from the relatively massive supports for the wire, so as to provide the necessary ionization at these points.

With the foregoing objects in view, and others which will become apparent as the description proceeds, my invention consists in the systems, methods, apparatus and combinations hereinafter described and claimed, and illustrated in the accompanying drawing, wherein:

Figure 1 is a longitudinal vertical sectional view of an exemplary form of embodiment of my invention, the section plane being indicated at 1-1 in Fig. 2;

Fig. 2 is a vertical cross-sectional view, on the plane indicated by the line III[ in Fig. 1, with parts broken away for clarity of illustration; and,

Fig. 3 is a top plan view, with parts broken away for clarity of illustration.

In the illustrated embodiment of my invention, which is only one of many forms which the invention can take, air to be treated is drawn in through the top of the precipitator-cabinet I through a protective screening 2, and passes downwardly through an ionizing chamber 3 in the top of the cabinet, after which the air continues downwardly and passes through a precipitating chamber 4, the bottom of which discharges into a blower 5 for drawing the air through the apparatus. The outlet of the blower may either discharge the treated air near thefloor or the treated air may be led away from the blower by any means and in any manner which may commend itself as desirable.

The ionizing chamber usually comprises a plurality of ionizing units disposed transversely with respect to the direction of air-flow, each ionizing unit consisting of a centrally disposed fine wire 6 which is disposed in spaced relation between two relatively large electrodes I which are preferably tubular or curved in section, so that they present curved surfaces toward the ionizing wire, as eigplained in my aforesaid application. As explained in my aforesaid application, now Patent 2,129,783, the relatively large electrodes I are of limited extent in the direction of gas-flow, and have an effective tubular surface having a radius of curvature which is large at all points of said efiective surface as compared to the radius of curvature of the fine wire 6. The tubular electrodes I are grounded on the precipitator-cabinet I. The ionizing wires 6 are suspended between rigid metal end-supports 8 carried by a skeleton framework 9 which is supported by insulators II. It is usually necessary to support each wire also at one or more intermediate points, as by means of rigid metal intermediate supports I2 which are also carried by the skeleton framework 9.

According to my invention, I provide means for producing an adequate fiow of ionizing current at the supporting points where the wires 6 are engaged by their respective supports 8 and I 2. In the case of the end-supports 8, it will be noted that these supports must be adequately spaced from the end walls I3 of the cabinet, in order to provide adequate insulation, and hence some of the air may pass between the supports 8 and the end walls l3, as well as between said supports and the two tubular electrodes 1 which are on either side of the wire. To provide the necessary ionization at these points, I solder short pieces of Wire l4 sticking out in the three directions from the end-supports 8, near the points where the wire 8 is attached, so as to provide one prong extending toward the end wall l3 of the cabinet, and another prong extending toward each of the associated tubular electrodes 1 between which the wire is disposed. These wire-prongs I4 may be suit-.

ably designed to meet the conditions encountered in any particular equipment. A successful form of embodiment of the invention utilizes wireprongs of 22 mils diameter extending about threequarters of an inch from the center of the support 8, although I am not limited to any particular dimension. In case of the intermediate supports l2, only the laterally extending wire-prongs l5 are needed, extending toward the two tubular electrodes 1.

The precipitating chamber 4 consists of a large number of spaced insulated plates 20 and grounded plates 2|, spaced closely together, and disposed parallel to the direction of air-flow. The insulated precipitating plates 20 are supported by notched metallic supports 22 which are carried by insulators 23. The non-insulated precipitating plates 2| are supported and spaced by means of notched plates 24 carried by the cabinet I.

As explained in my aforesaid application, the ionizing wires 6 and the insulated precipitatorplates 20 are unidirectionally charged with respect to the uninsulated or grounded parts. Because of the greater spacing between each wire 6 and its associated tubular electrodes 1, as com pared with the spacing between the alternate plates 20 and 2| of the precipitator chamber, the ionizing voltage is frequently higher than the precipitating voltage. As explained in my aforesaid application, now Patent 2,129,783, the relatively close spacing between the precipitator.

plates 20 and 2| usually makes the potentialgradient in the spaces between said plates in excess of the average gradient in the ionizing space. I have indicated that unidirectional voltages are applied to the ionizing wires 6 and the precipi tator-plates 20 by showing leads 25 and 26, respectively, marked on the drawing as being energized, respectively, by the positive terminal of the unidirectional ionizing source of voltage I+, and by the positive terminal of the unidirectional precipitating source of voltage P+, the negative terminals (-l being grounded on the frame of the cabinet I, as indicated at 30.

In operation, the air entering the top of the cabinet I, as shown by the arrows, is first ionized in the ionizing chamber 3, so as to charge the particles which are suspended in the incoming air. The air then passes through the precipitating chamber 4 where the charged suspended particles become attracted to the oppositely charged precipitating plates, after which the purified air is withdrawn from the cabinet by the blower 5. When the precipitator, particularly the precipitating plates, become dirty by reason of the foreign particles extracted from the air, in the course of weeks or months, the precipitator may be taken outdoors and washed with a hose, after which it is again ready for use.

By my invention it will be observed that the efficiency of precipitation is increased by the measures which I have taken to combat the difliculties heretofore experienced as the result of dark regions along the ionizing wires 6, where inadequate ionization is obtained. When I refer to the dark regions around the supporting-points of the ionizing wire, as obtained in previous structures utilizing massive wire-supports 8 and I2, without means for providing supplementary ioniza'tion at these points, I refer to regions which appear to be dark when viewed in a dark room. Normally, there will be a slight discharge or corona-glow which is distinctly visible in a dark room, in the immediate vicinity of the ionizing wires 6, when the precipitator is operating correctly, but this phenomenon is distinctly different from the corona-discharge which is visible in sunlight, or even in weak daylight, and which requires a much higher ionizing voltage than I utilize on my wires 6. I term the lowest voltage which produces a corona-discharge of the sort which is visible in sunlight or in weak daylight the critical corona voltage of the wire. My present invention follows the practices explained in my aforesaid application, in utilizing an ionizing voltage which is considerably lower than this critical corona voltage, this practice being made.

possible by the utilization of a sufiiciently fine ionizing wire. When I refer to dark spaces appearing around the ionizing wire, therefore, I refer to spaces which seem dark in a darkened room, and not to spaces which seem dark in the sunlight.

While I have described my invention in a preferred form of embodiment, and have suggested certain limits in accordance with my best understanding of the same at the present time, I desire it to be distinctly understood that I am not altogether limited to these limits or understandings, or to the particular form of embodiment shown in the drawing. I desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language and the prior art.

I claim as my invention:'

1. A gas-purifying precipitator comprising an ionizing chamber, a separate precipitating chamber, and means for causing a gas-flow successively through first said ionizing chamber and then said precipitating chamber; said ionizing chamber being provided with one or more ionizing units, each unit being disposed transverse to the gas-flow and comprising a single insulatedly supported fine wire spaced between substantially unin'sulated relatively large electrodes, a plurality of relatively rigid supporting-members for insulatedly supporting said fine wire, and additional ionizing means at one or more of the supportingpoints of the fine wire for ensuring the copious ionization of the portion of the gas which flows past the vicinity of said one or more supporting: points; said fine wire or wires being of less than 32 mils diameter and being of such fineness that substantially utilizable ionization of suspended particlesin the gas is obtained at a wire-charging voltage below the critical corona voltage, and the wire-charging voltage being below said critical corona voltage.

2. A gas-purifying precipitator comprising an ionizing chamber, a separate precipitating chamber, and means for causing a gas-flow successively through first said ionizing chamber and then said precipitating chamber; said ionizing chamber being provided with one or more ionizin units, each unit being disposed transverse to the gas-flow and comprising an insulatedly supported wire spaced between substantially uninsulated relatively large electrodes, a plurality of relatively rigid supporting-members for insulatedly supporting said wire, and additional ionizing means at one or more of the supporting-points of the wire for ensuring the copious ionization of the portion of the gas which flows past the vicinity of said one or more supporting-points.

3. A gas-purifying precipitator comprising an ionizing chamber, a separate precipitator chamber, and means for causing a gas-flow successively through first said ionizing chamber and then said precipitator chamber; said ionizing chamber being provided with one or more ionizing gas-flow and comprising tively large electrodes and a single insulatedly supported relatively small electrode disposed between the pair of large electrodes, the relatively small electrode being a fine wire of less than 32 mils diameter, a plurality of relatively rigid supporting-members for lnsulatedly supporting said fine wire, and additional ionim'ng means at one or more of the supporting-points of the fine wire for ensuring the copious ionization of the portion of the gas which flows past the vicinity of said one or more supporting-points; the relatively large electrodes being of limited extent in the directlon of gas-flow and having an efiective surface having a radius of curvature which is large at all points of said effective surface as compared to the radius of curvature of the fine wire, and means for unidirectionally charging said fine wire relative to said large electrodes, whereby foreign particles in the air are charged by the fine wire.

GAYLORD W. PENNEY.

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