US2357355A - Electrical dust precipitator utilizing liquid sprays - Google Patents

Description

Sept. 5, 1944. G. w. PENNEY ELECTRICAL DUST PREGIPITATOR UTILIZING LIQUID-SPRAYS Filed May 13, 1941 INVENTOR @/a /f /z e/vflj ATTORNEY WITNESSES:

Patented Sept. 5, 1944 ELECTRICAL DUST PRECIPITATOR UTILIZ- ING LIQUID SPRAYS Gaylord W. Penney, Wilkinsburg, Pa., asslgnor ,to

Westinghouse Electric 3; Manufacturing Lompany, East Pittsburgh, Pa., a corporation of Pennsylvania Application May 13, 1941, Serial No. 393,190

12 Claims.

My invention relates to electrical gas-cleaning precipitators or similar apparatus for removing dust or dust-particles from gaseous streams, by

dust or dust-particles meaning any discrete foreign particulate matter capable of being removed from a gas by electrical means and methods.

In my copending application Serial No. 393,189, filed concurrently herewith and entitled Electrilied liquid-spray dust-precipitator," I disclose systems for cleaning a dust-laden gas stream by electrically charging the dust-particles in the gas and then mixing the gas and the charged dust particles therein with a liquid-spray having its spray-drops charged with a polarity opposite to that on the charged dust-particles. In the systems disclosed in the aforesaid application, the

dust-particles are charged by passing the dustladen gas through a suitable electrostatic field, and the liquid-spray is charged through the action of a substantially non-ionized electrostatic field having a high field concentration at the spray-nozzle or other spray-means for producing the spray, the spray-charging field being produced by utilizing the spray-means as one electrodemeans and a relatively insulated loop or loops about the spray-means as a second oppositely charged electrode-means, the spray-means and the loop or loops being in the gas-conduit and the spray-drops taking a charge of the polarity of the spray-means. In the spray region, which is the region in which the gas and the charged dust-particles therein are mixed with the oppositely charged liquid spray-drops, dust-particles apparently are transferred to the spray-liquid, for by subsequently separating the spray-liquid from the gas, the dust-particles have been found to be in the spray-liquid.

The primary object of the present invention is to provide other systems, operating generally in accordance with the principles and teachings of the systems disclosed in my aforesaid application, which will have many of the advantage; disclosed in the aforesaid application, but which utilize somewhat different but desirable features and arrangements and which it was considered desirable to disclose in a separate application.

One of the objects of the present invention is to provide a means for electrifying or charging the liquid-spray, which means will adequately and completely charge the spray-drops.

It is another object of this invention to provide a gas-treating precipitator of the type described in which the spray-drops are charged by passing the spray through an ionizing electrostatic held, by ionizing electrostatic field meaning a field which spatially contains charged matter, such as electrons, ions, or charged molecules, or combinations thereof, and, consequently, includes a spatially ionized region.

It is another object of my invention to provide a gas-cleaning apparatus of the type described in which the spray-drops are charged through the action of an ionizing electrostatic field of a polarity opposite to that of the electrostatic field utilized to charge the dust-particles, but the spray charging ionizing field being so confined or arranged that oppositely charged dustparticles in the gas stream do not have their charges neutralized by the spray-charging field before they can mix with the charged spraydrops.

It is an important object of my invention to provide a charged spray in the path of the gas carrying charged dust-particles, which spray will present a substantial curtain of some depth completely across the gas-stream so that the charged spray-drops and the charged dust-particles will have an adequate opportunity to react to the end that the gas is cleaned, whereby an increased gas flow velocity can be utilized.

In one form of my invention, a dust-precipitator means is disposed in the gas-conduit after the dust-charging zone, and comprises a nondischarging electrode-means which cooperates with an ionizing electrode-means to produce an ionizing electrostatic field through which the spray flows so that the spray-drops are charged with a polarity which is the same'as that of the ionizing electrode-means. The non-discharging electrode-means takes the form, in this embodiment, of a conducting shield around the spray nozzle which can, if desired, also be pa t of the non-discharging electrode-means; and the ioniz-- ing electrode-means takes the form of a discharging or ionizing pointed rod.

The polarity of the ionizing point of the rod is of opposite sign to that of the ionizing electrode-means of the dust-charging field; and since the ionizing point and non-discharging electrodemeans and nozzle associated therewith are in the gas-stream, producing an ionizing electrostatic field of charged matter predominately opposite in sign to the field charging the dust-particles, it is desirable to prevent th neutralization of some or all of the charge on the dust-particles before they mix with the oppositely charged spray-drops. To this end a battle means can be provided diverting the gas-stream from the spray-charging field, but the non-discharging electrode-means for the spray-charging field can readily be adapted to this purpose so that this electrode-means may also act as such a battle-means. For this double purpose of the non-discharging electrode-means, the conducting shield is made in the shape of an umbrella which partially encompasses the associated discharging point or points of the spraycharging ionizing means, but is spaced from the discharging point or points and relatively insulated with respect thereto. By this expedient, the spray drops can be charged by a spray-charging ionizing electrostatic field enveloped by the gas-stream, but the charged dust-particles in the gas-stream mix with the charged spray-drops outside of the main portion of the spray-charging ionizing electrostatic field and without the risl; of charged dust-particles being partially or completely neutralized solely by the action of the spray-charging spatially ionized electrostatic field.

However, the gas-flow may be somewhat disturbed because the electrode-means for the spray-charging ionizing electrostatic field are in the gas-conduit. Consequently, in other forms of my invention, the ionizing electrode-means and the non-discharging electrode-means for creating the spray-charging ionizing electrostatic field are not disposed in the main gas-conduit, thereby eliminating obstacles or resistance to the gas-flow.

The particular liquid used as the dust-removing spray is subject to wide choice. Economical reasons and operating considerations indicate that ordinary tap-water can be used for the spray-liquid with high cleaning efficiency, and such a liquid is especially desirable for cleaning air to be breathed. In some instances the liquid may be treated in order to improve its wetting properties or even its hygroscopic action, as more particularly described in my aforesaid application. Ordinary oils, which are insulating,can,be used for spray-liquids for precipitators embodying my invention, and have the advantage of being viscous so that dust-particles will readily stick. to the spray-drops. However, an oil should not be used as a spray liquid if such use is accompanied by an explosive hazard, such as would be the case under certain conditions involving an oil mist or spray in the presence of oxidizing gases.

Other features, objects, mod.fications and innovations of my invention, in addition to those specifically recited herein and in my aforesaid application, will be apparent from the accompanying drawing-which shows, more or less diagrammatically, the essential novel elements of the instant embodiments of my invention.

In the drawing:

Figure 1 is a vertical sectional view to a part of a, gas-conduit means incorporating one form of my gas-cleaning system?" Fig. 2 is a vertical sectional view of part of a gas-conduit means incorporating another form of my invention; and

Figs. 3 and 4 are vertical sectional views of further embodiments of my invention.

In general my invention is adapted to be associated with, or to include, any suitable gasconduit means which provides or defines a gasflow path for a gas-stream; and in Fig. l the precipitator comprises part, or all, of a gasconduit means, indicated in its entirety by the reference numeral 2, the direction of 'gas-fiow therethrough being in the direction of the arrows shown in'the embodiments herein described. The gas-conduits are assumed to be of vention is not necessarily limited thereto and can be used, with suitable adaptations, to gasconduits of circular or other forms.

The precipitating apparatus comprises a dustcharging zone i in which the dust-particles in the dust-laden gas are charged, and a precipitating zone 5 on the downstream side of the dust-charging zone.

The dust-charging means includes an ionizing-means comprising a plurality of relatively insulated discharging and non-discharging electrode-means extending transversely across the gas-conduit 2 at the dust-charging zone, and

1 may take the form of the ionizing means disrelatively rectangular cross-section but my inclosed in the E. H. R. Pegg Patent No. 2,215,298 issued September 17, 1940. The discharging electrode-means comprises one or more insulatedly supported ionizing-wires 6 each of which is spaced from and between a pair of tubular, ground electrodes Z3 which are grounded, the gas-conduit 2 being also grounded, as indicated at id.

The precipitating means comprises a spraymeans and spray-charging means for producing a liquid-spray and charging the spray-drops of the spray. However, these operations may be performed simultaneously by a cooperating relationship of the elements comprising the spraymeans and the spray-charging means so that the two functions of producing the spray and charging the sprayedrops can be performed by one or more single means. The spray-means comprises a liquid supply-pipe l2 having one or more spray-nozzles l6 through which liquid flowing through the supply-pipe lfiis'discharged in the form of a spray in such manner that the spray ultimately occupies or spreads across the full transverse area. of the gas-conduit 2. Each spray-nozzle IQ is surrounded by, and in direct contact with, a non-discharging electrode-means in the form of a shield l5 which has an umbrella shape and encompasses a discharging electrodemeans in the form of metallic pin or rod it or the like, terminating in a sharp point 28 spaced from and substantially symmetrically spaced with respect to the associated shield l6.

The rods l8 are supported on a metal rod 22 carried on an insulator 26 so that the discharging electrode structure is insulated from the gas-conduit 2 and the shields 55 which are preferably of metal and conductively connected to the spray-nozzles i l of the supply-pipe 52, both of which are also of metal and grounded to the gas-conduit 2. 0 An insulated conductor 26 is connected to the ionizing wires 6, and an insulated conductor 28 is connected to the supporting rod 22.

' The precipitating zone further comprises suitable expedients for separating the spray-liquid from the gas-stream after the charged dust-particles and the oppositely charged spray-drops have had a suitable opportunity to react to cause the dust-particles to follow the spray-liquid. Charged spray-drops will be collected on the metallic walls of the gas-conduit 2 and also on a plurality of grounded spaced electrodes 30 extending across the gas-conduit 2. Spray-liquid ing bottom member 48 below the gas entrance of the gas-outlet pipe 32 may be sloped to the spout 34.

A suitable unidirectional source of electrical energy may be used to energize the ionizing electrode-means of the dust-charging zone 4 and of the precipitating zone 5, and this is indicated. by the plus sign to the conductor 26 and they minus sign' to the conductor 28. The ionizing wires 8 can be made positive with respect to the gas-conduit 2 and the ionizing points can be made negative with respect to the gas-conduit 2 by grounding an intermediate point of the voltage supply. 'Many suitable connections can be used, and I have shown a simple expedient for oppositely charging the ionizing means of the dust-charging zone 4 and of the precipitating zone 5, which comprises a voltage-divider resistor 42 across the conductors 26 and 28, having an intermediate point 44 grounded at "I,

.and which is preferably at the midpoint of the resistor 42. 1

The dust-laden gas-stream first passes through the dust-charging zone 4 wherein the dust-particles in the gas are positively charged. The spray-drops from the spraymozzle l4 are charged in the ionizing electrostatic field established between each ionizing point 20 and associated shield It so that the spray-drops will be charged negatively. However, the charged dust-particles are diverted or deflected from the field between the ionizing points 20 and shields l6 because of the action of the shields as gas-flow baflies. In the spray-region on the downstream side of spray-charging field, the-spray spreads across the gas-conduit 2 so that the gas mingles or mixes with the spray and the charged dustparticles in the gas react with the oppositely charged spray-drops and apparently attach themselves thereto. the dust-laden spray-liquid from the cleaned gas-stream by the means described provides cleaned gas in the gas-outlet pipe 32. The grounded plates 30 which collect part of the spray-drops so that spray-liquid flows down-.

wardly thereon, also limits the space-charge in the spray-region. a

In the embodiments shown'in Figs. 2, 3 and 4, the spray-means and spray-charging means are disposed at one side of the gas-flow path so as not to interfere with the flow of the gasstream. These embodiments also differ from the embodiment shown in Fig. 1 in that a different ionizing means is provided for charging the spray-drops.

In the embodiment shown in Fig. 2 a gas-conduit 60, which is grounded as indicated at 52, has a somewhat angular shape and is provided with a closed spray-chamber 54 at one side of the gas-conduit near a bend in the gas-conduit ill.

the dust-charging zone 4 oi the embodiment shown in Fig. 1, is disposed in the gas-conduit- A dust-charging zone 56, similar to Subsequent separation of ing-wires of the former are so energized that they are at a polarity opposite to that of the ionizing-wires of the latter. In Fig. 2 the ionizing-wires of the dust-charging zone 4 are energized to be negatively charged, and the ionizingwires of the spray-charging zone are energized to be positively charged, but the charging effects of the dust-charging ionizing electrostatic field and the spray-charging ionizing electrostatic field in this embodiment, as are the other embodiments herein described, may be reversed.

The spray is established and charged outside of the main gas-stream and is introduced across the gas-stream in the region below the bend in the gas-conduit 50 so that a substantial curtain of some depth is introduced across the gas-stream at an angle to its general direction of movement. Suitable means for decreasing the space-charge in the spray-region and for separating the spray-liquid from the gasstream after the charged dust-particles have mixed with the oppositely charged spray-drops can be provided and, may follow the means shown in Fig. 1.

Fig. 3 is similiar to the embodiment shown in Fig. 2 except that the charged spray is projected substantially perpendicularly across the gas-stream in the gas-conduit 10, for mixing with the gas-stream after the latter has passed through the dust-charging zone 12. Fig. 4 shows a further embodiment in which the gas-conduit I6 is provided with analmost right-angular bend so that the charged spray is introduced into the gas-streamwith the general direction of movement of the spray substantially parallel to the general direction of movement of the gasstream in the downstream leg 18 of the gasconduit 16.

While I have described my invention in certain preferred embodiments thereof, it is obvious that many modifications might be made thereto, and equivalent constructions provided.

I claim as my invention:

l. Continuously operable electrostatic precipi-' tating means for continuously removing foreign particles from a gas-stream and from the duct through which said gas-stream is flowing, com- "trode, said spray-charging electrodes being spaced from each other, and means for maintaining a unidirectional potential-difierence between said electrodes for producing a spacial ionizing electrostatic field therebetween for charging the spray-drops to a potential opposite to that of said ionized foreign particles in the gas-stream; both the spray, as it first leaves said spray-discharge means, and the spray-charging ionizing electrostatic fleld being out of the main gas-stream path, but the spray being so directed that it i'irstpallea through said spray-charging ionizing electrostatic field and then extends across the gas-stream carryingsaid ionized foreign particles; and spraysprayed liquid from the commingled liquid-spray and gas-stream, and withdrawing said liquid from the gas-stream duct.

2. The invention as defined in claim 1, characterized by said spray-discharge means and said discharging electrode being. in a spraychamber at a side of the gas-flow path in said duct.

3. The invention as defined in claim 1, characterized by said spray-discharge means being in the path of the gas-stream carrying said ionized foreign particles but being provided with a shield for causing the main body of said gas-stream to bypass said spray-discharge means and its spraycharging ionizing electrostatic field.

4. The invention as defined in claim 1,- characterized by said spray-discharge means being inthe path of the gas-stream carrying said ionized foreign particles, and the non-discharging electrode of its spray-charging means being in the form of a shield for causing the main body of said gas-stream to bypass said spray-discharge means and its spray-charging ionizing electrostatic field.

5. Liquid-spray apparatus for causing a charged liquid-spray to be distributed across the path of a gas-stream, said liquid-spray apparatus comprising a pipe-means, one or more spray-discharge means associated with said pipe-means for delivering a liquid-spray, one or more spraycharging means comprising a discharging elec trode and a cooperating non-discharging electrode, said electrodes being spaced from each other, and means for maintaining a unidirectional potential-difference between said electrodes for producing an ionizing electrostatic field therebetween for charging the spray-drops, said nondischarging electrode being in the form of a shield for causing the main body'of the gasstream to bypass said spray-discharge means and its spray-charging ionizing electrostatic field.

6. Continuously operable electrostatic precipitating-means for continuously removing foreign particles from a gas-stream and from the duct through which said gas-stream is flowing, comprising the combination, with said gas-stream duct, of ionizing-apparatus for ionizing foreign particles in said gas-stream, whereby said foreign particles are ionized with a predetermined potene tial-polarity; liquid-spray apparatus for causing a charged liquid-spray to be distributed across the path of the gas-stream carrying foreign par ticles ionized by said ionizing apparatus, said liquid-spray apparatus comprising spray-dis charge means for delivering a liquid-spray, one or more spray-charging means comprising a discharging electrode and a cooperating non-dis charging electrode, said electrodes being spaced from each other, and means for maintaining a unidirectional potential-difference between said electrodes for producing an ionizing electrostatic field therebetween for charging the spraydrops with a potential-polarity opposite to that of the said ionized foreign particles in the gasstream; both the spray, as it first leaves said spray-discharge means, and the spray-charging ionizing electrostatic field being out of the main gas-stream path, but the spray being so directed that it first passes through said spray-charging ionizing electrostatic field and then extends across the gas-stream carrying said ionized foreign particles; and spray-separation means for separating dust-carrying sprayed-liquid from the commingled liquid-spray and gas-stream, and withdrawing said sprayed-liquid from the gas-stream duct.

7. The invention as defined in claim 6, characterized by said spray-discharge means and said discharging electrode being in a spray-chamber at a side of th gas-flow path in said" duct.

8. The invention as defined in claim 6, characterized by said spray-discharge means being in the path of the gas-stream carrying foreign particles ionized by said ionizing-apparatus but being provided with a shield for causing the main body of the said gasstream to bypass said spray-discharge means and its spray-charging ionizing electrostatic field.

9. The invention as defined in claim 6, characterized by said spray-discharge means being in the path of the gas-stream carrying foreign particles ionized by said ionizing-apparatus, and the non-discharging electrode of its spray-charging means being in the form of a shield for causing the main body of the said gas-stream to bypass said spray-discharge means and its spray-charging ionizing electrostatic field.

10. In gas-treating apparatus, means for producing an electrically ionized spray, comprising a pipe-means, one or more nozzle-means associated with said pipe-means for delivering said spray, a non-discharging electrode immediately back of each nozzle-means, one or more pointed electrodes in front of, spaced from, and pointing towards, each nozzle-means, and means for applying a unipotential potential-difference between said non-discharging electrode or electrodes and said pointed electrode or electrodes for producing an ionizing electrostatic field therebetween for charging the spray-drops.

11. The invention as defined in claim 1, char acterized by the said spray-discharge means comprising a nozzle-means on the far side, with respect to the gas-stream, of the main ionizing electrostatic field between the spray-charging electrodes, for establishing the spray outside of said main ionizing electrostatic field.

12. The invention as defined in claim 6, characterized by the said spray-discharge means being on the far side, with respect to the gas-stream, of the main ionizing electrostatic field between the spray-charging electrodes, for establishing the spray outside of said main ionizing electrostatic field.

GAYLORD W. PENNEY.

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