US2523618A

US2523618A - Electrostatic apparatus

Info

Publication number: US2523618A
Application number: US705332A
Authority: US
Inventors: Gilman Samuel
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1945-02-09
Filing date: 1946-10-24
Publication date: 1950-09-26
Anticipated expiration: 1967-09-26

Description

Sept. 26, 1950 s. GILMAN ELECTROSTATIC APPARATUS Original Filed Feb. 9, 1945 INVENTOR L i 0 G a z Y. M 3 5 Patented Sept. 26, 1950 UNITED, STATES PATENT OFFICE ELECTROSTATIC APPARATUS Original application February 9, 1945, Serial No.

Divided and this application October 24, 1946, Serial No. 705,332

18 Claims.

This application is a division of my patent application, Serial No. 577,021, filed February 9, 1945.

My parent application is directed to apparatus for removing foreign particulate matter from a gas stream by means of equipment that produces an electrically charged liquid spray having a higher net electric charge than was previously obtainable with similar equipment such as disclosed, for example, in G. W. Penney Patent No. 2,357,354, dated September 5, 1944. Various embodiments are disclosed in the parent case. The instant application is limited to selected embodiments in which a charge is imparted to a liquid spray by the use of elongated electrodes.

Objects, features and innovations of my invention, in addition to those set forth in my aforesaid parent application, will be discernible from the following description which is to be taken in conjunction with the accompanying schematic drawing, in which: c

Figure 1 is a vertical sectional view of an electrical dust-precipitator embodying a form of my invention;

Figs. 2 and 3 are sectional views, taken substantially along the lines IIII and IIIIII, respectively of Fig. 1

Fig. 4 is a vertical sectional view of a further form of my invention;

Fig. 5 is a view showing another apparatus in accordance with my invention, for producing charged sprays; and 7 Fig. 6 is an enlarged sectional view, taken substantially on the line VI--VI of Fig. 5.

The apparatus shown in Figs. 1, 2 and 3 comprises a rectangular gas duct 68 in which is located a dust-charging or ionizing means A for charging gas-borne particulate matter, and a dust-precipitating means B on the downstream side of the dust-charging means, for removing the charged particles from the flowing gas stream. Field affecting means C comprising a plurality of spaced grounded plates may be provided on the downstream side of the dust-precipitating means B for preventing space discharges and for improving dust removal.

The dust-charging means A comprises a plunality of spaced grounded relatively large tubular electrodes Ill, transverse to the gas stream, and between which relatively ilne ionizing wires 12 ar insulatedly supported. Such a dust-charging means, or ionizer element, is comparatively well known to the art.

The dust-precipitating means B comprises a 2 means being indicated in its entirety by the reference numeral 14. The charged-spray-producing means 14 comprises any suitable equipment which emits a liquid spray, and is shown as a 5 metallic pipe-member It provided with a plurality of metal nozzles 18 along its length. The tips of the nozzles are kept at ground potential by grounding the pipe-member 16 or conductively associating it with the gas duct 69 which is preferably of metal and also grounded. The spray from the nozzles 18 passes between a pair of spaced straight parallel semicylindrical electrodes 82 which are supported on insulators 83 and are given a relatively high potential through insulated conductors 84 connected to any suitable power source. Such a source is indicated schematically as a battery 85 having on terminal end grounded. The curved surfaces of the electrodes face the nozzles in the embodiment shown.

20 The potential-polarity of the ionizing wires 12 and the electrodes 82 is the same and is opposite to that of the electrodes 10 and the nozzles 18. The ionizing wires 12 produce charged matter in the spac between them and the ground elec- '25 trodes Iii so that gas-borne particles are charged.

Liquid fed to the pipe-member 16 comes out of the nozzles 18 as a spray with its droplets charged because of the electrostatic field between the noz- Zles and the electrodes 82. Consequently, each nozzle-tip from which a spray emits is, in effect,

an electrode that is charged oppositely from the electrodes 82. The spray droplets have electric charges of a sign or polarity which is opposite to that on the gas-borne particles so that the droplets and particles attract each other in the region where they intermingle, this region being generally somewhat below the electrodes 82. Preferably th charged spray spreads completely across a full transverse section of the gas duct,

40 at the field affecting means C. The effectiveness with which the spray droplets are charged, and hence the efficiency of the dust-precipitator in the embodiments described, can be increased by preventing drops which collect on the electrodes 82 from continually discharging into the spray region or toward the nozzles 18, for reasons more fully described in my aforesaid parent application. To this end, in the embodiments disclosed in Figs. 1, 2 and 3, the liquid drops collecting on the electrodes 82 are caused to discharge toward means for producing a charged-spray, the last electrode sumcient to electrically force the col- 3 lected drops on the electrodes to discharge toward the side 06 which functions as an electrode charged oppositely to the associated electrode 02. After a drop on an electrode 02 discharges and before it recharges, it will fall from th electrode if the drop has suflicient weight.

In Fig. 4, I show a further embodiment which is similar to that of Figs. 1-3 but in which the action of gravity is utilized to help remove drops from electrodes 90 that correspond to the electrodes 02 of Fig. 1. Electrodes 90 slope downwardly so as to caus drops thereon to tend to flow downwardly to the lowermost ends of the electrodes, away from the spray region so that they cannot discharge into the spray. Sloping the electrodes permits the spacing between the electrodes and the parallel sides of the gas-duct to be greater than would be the case if the electrodes were not sloped.

Figs. 5 and 6 show a further form of my invention in which straight parallel cylindrical elongated relatively insulated electrodes I00 are provided between which a metallic spray-producing means I02 establishes a spray. In this embodiment, the spray-producing means has been shown as pneumatic and comprises a grounded liquid-supply pipe-member I04 and an air-supply pipe-member I06 connected to a plurality of spray nozzles I08 having outlet tips H0. Liquid flows centrally through each spraying nozzle via a passage II2. Air under pressure flows in a conical passage I which is around the passage 2 and is tapered to the outlet tip IIO for providing a spray which passes between the insulated electrodes I00.

Ihe electrodes I00 are sloped as in the embodiment shown in Fig. 4. However, the lowermost end of each is provided with a small catch-basin I I6 having a drain-opening to which a drain-pipe H0 is connected through which liquid collecting on the electrode may drain. The drain-pipe III is of a material providing a high resistance path along which the draining liquid flows into a grounded container I20.

In embodiments usually utilizing a high resistance drain, the liquid remaining on the insulated electrodes, such as the electrodes I00, loses electric charge by leakage so that the possibility of electrical discharge from distorted liquid drops on the electrodes is greatly minimized or entirely eliminated. In embodiments which do not use a drain, liquid on the electrodes can fall from them after they form large enough drops on which the pull of gravity is greater than the force exerted on them by the electrostatic field extending from the electrode to the spray-nozzles and to the point at which the charge of the spray may be considered to be concentrated.

I have found that the use of substantially straight electrodes, either cylindrical or semicylindrical or some other cross-section, in equipment for charging a spray, is a considerable improvement over the ring-type electrodes, particularly if used with a plurality of spray-nozzles of a pneumatic type along the lines shown, for example in Figs. 5 and 6.

Using a pneumatic nozzle, identified as type JPNF, set-up No. 12, described in a catalogue identified as Spraying System Nozzles and Related Products, Catalogue No. 22 oi the Spraying System Company, Chicago, Illinois, an improvement of as much as 200% and above in the charge given to the spray was obtained over that obtained in the specific non-pneumatic type of spray-nozzle and ring electrode, specifically dethem. By sloping the electrodes about 20 to the,

horizontal, instead of keeping them horizontal. very effective draining of collected liquid was provided, permitting a much higher voltage between the spray-nozzle and the electrodes before objectionable drop discharges occurred.

The diameter of the straight electrodes and their spacing aflect the size of the drops on the electrodes and the amount of charge that can be given to the spray. With a constant voltage across the tubular electrodes and the spray-discharge nozzle, increasing the separation of the electrodes aflects the field-gradient at the nozzle tip and at the surface of the electrodes. The factors aflecting the field-distribution are, however, so varied and complex that an exact analysis is hardly practical. Various grounded surfaces around the nozzle and the relatively insulated electrodes obviously will change the field lines. Even the character and angle of the spray have their eflect. However, experiments indicated that for a particular apparatus there appears to be an optimum spacing for straight electrodes at which a maximum charge is imparted to the spray.

While I have described my invention in connection with several embodiments, it is obvious that its teachings have wide application and can be applied in other forms or uses.

I claim as my invention: a

1. A device of a class described comprising, in combination, a duct-means for a gas-stream, charging-means for charging gas-borne particles, a liquid-spraying device on the downstream side of said charging-means, an insulated electrodemeans in said duct-means spaced to permit the spray from said liquid-spraying device to pass in proximity thereto and then spread across the duct-means, and a high-resistance drain for draining oiI liquid collecting on said insulated electrode-means.

2. A device of a class described comprising, in combination, a duct-means for a gas-stream, charging-means for charging gas-borne particles, a liquid-spraying device on the downstream side of said charging-means, a sloped elongated electrode-means in said duct-means spaced and insuiated from said liquid-spraying device, means for oppositely charging said liquid-spraying device and said electrode-means, and drain means from the lower end of said electrode-means.

3. Charging apparatus comprising a sprayingdevice having a plurality of spaced points from which a plurality of sprays can be emitted, a pair of spaced elongated parallel electrodes spaced from said points near outer opposite sides of the region for the sprays, said electrodes being relatively insulated from said points, and means for supporting said electrodes so as to substantially span the distance between said points, said electrodes being substantially straight, and sloping with respect to a line joining a pair of said points.

4. Charging apparatus comprising a sprayingdevice having a plurality of horizontally spaced points from which a plurality of pneumatic sprays can be emitted, a pair of spaced elongated metal electrodes spaced from said points near outer opposite sides of the region for the sprays, said elecasaaeia.

and means for supporting said electrodes so as to substantially span the distance between said points, said electrodes being substantially straight and supported so as to slope downwardly, said points being spaced from a plane which Joins the edges of said electrodes farthest from said points, the points being spaced from said plane in a direction opposite to the direction in which the sprays leave said points.

5. Apparatus for providing a charged liquid spray, comprising a spraying-device having a plurality of horizontally spaced pneumatic sprayproducing nozzles having tips from which a plurality of sprays can be emitted, and a pair oi. spaced separate electrodes spaced from said tips and spanning the distance therebetween near outer opposite sides of a region occupiable by the sprays, said electrodes being relatively insulated from said nozzles, said nozzles pointing between said electrodes and having their tips spaced from said electrodes in the direction opposite to the spraying direction.

6. The invention of claim characterized by said electrodes being substantially straight and sloping with respect to a line Joining a pair oi said points.

7. Apparatus for providing a charged liquid spray, comprising a spraying-device having a plurality of spaced pneumatic spray-producing noz zles from which a plurality of sprays can emitted, said nozzles having tips, a pair of spaced substantially straight electrodes spaced from said tips both laterally and in the spraying direction and spanning the distance therebetween, said electrodes being transversely curved at faces located at outer opposite sides of a region occupiable by the sprays, said electrodes being relatively insulated from said nozzles, said nozzles pointing between said electrodes, additional electrode-means relatively insulated from said pair of electrodes, and arranged on a side thereof away from said region, and means for oppositely charging said electrodes with respect to said nozzles and said electrode-means, the spacing, configuration and charging-potentials of said electrodes, electrode-means, nozzles and charging means being such that the field gradient at said electrodes in a direction toward said region is less than the field gradient at a part of said electrodes iacing in a direction away from said region.

8. A device of a class described comprising, in combination, a rectangular metallic dustmeans for a gas-stream, charging-means for charging gas-borne particles, a liquid-spraying device on the downstream side of said chargingmeans, a pair of separate parallel insulated rodlike electrodes in said duct-means spaced to permit a spray from said liquid-spraying device to pass therebetween and then spread across the duct-means, said electrodes paralleling opposite v said electrodes.

10. Means for producing a charged liquidspray comprising spray means providing a plurality of spray-emitting points arranged substantially linearly, insulated electrode-means ing with respect to the direction of gas-flow past insulated and spaced. from said points of said spray means, said electrode-means comprising substantially parallel spaced metal rod-like portions spanning the points, said portions being unconnected in the spanning distance, said spray-emitting points 01 said spray means being spaced from the plane nearest thereto which includes said metal portions of said electrodemeans, a second electrode-means comprising sections insulated from said portions and located near a side thereof away from said points, and means for oppositely charging said insulated electrode-means and said spray means, and for oppositely charging said insulated electrodemeans and said second electrode-means, the spacing, configuration and charging potentials being such that the tendency of the field gradient at said insulated electrode-means in a direction toward said spray means to cause liquid-drops on said insulated electrode-means. to deform and discharge toward said space, is overbalanced.

11. Means for producing a charged spray comprising a pair of elongated parallel metal electrodes, spraying nozzle-means having a spraying nozzle-tip insulated from said electrodes, said nozzle-tip being near the plane nearest thereto which includes a part of each of said electrodes, but lying on a side of said plane directed away from said electrodes, said nozzle-tip being directed to provide a spray in the space between said electrodes which spray is chargeable by an electric field between said nozzle-tip and said electrodes, said electrodes extending lengthwise beyond the nearest point of said nozzle-means for a distance greater than the distance of said nearest point to either of said electrodes.

12. Charged-spray-producing means as defined in claim 11 but further characterized by said electrodes being sloped from the direction in which said nozzle-means emits said spray.

l3. Charged-spray-producing means as defined in claim 11 but further characterized by additional electrode-means spaced from each of said electrodes on a side of each of said electrodes which faces away from said nozzle-tip, and voltage-applying means for oppositely charging said nozzle-tip and said electrodes and for oppositely charging said electrode and electrodemeans, the spacing, configuration and chargingpotentials being such that the field gradient at said electrodes facing in a direction toward said space is less than the field gradient at a part of said electrodes facing in a direction away from said space.

14. Charged-spray-producing means as defined in claim 13 but further characterized by said electrodes being sloped from the direction in which said nozzle-means emits said spray.

15. Means for producing a charged spray comprising a pair oi elongated rod-like substantially parallel electrodes, spray-nozzle-means having a spraying point insulated from said electrodes and providing a spray in the space between said electrodes, and chargeable by an'electric field between said spraying point and said electrodes, said electrodes being lengthwise substantially straight and transversely curved on the sides facing said spraying point, said spraying point being near a plane nearest thereto that in- 7 8 cludes a part of each of said electrodes, said REFERENCES CITED spraying mint lying on side of said plane The following references are 01' record in the ing away from said electrodes, said electrodes me of this patent:

extending lengthwise beyond the nearest point of said spraying nozzle-means for a distance UNITED STATES PATENTS greater than the distance of said nearest point 5 Number Name Date to either of said electrodes- 1,958,406 Dariah May 15, 1934 16. charged-spray-producing means as de- 2,207,576 Brown July 9, 1940 fined in claim 15 but further characterized by 2,357,354 Penney Sept. 5, 1944 pneumatic means associated with said nozzie- 10 means to provide a spray at said spraying point.

SAMUEL GILMAN.