US2598337A - Electrical precipitator - Google Patents

Description

May 27, 1952 G. E. ANDREWS ELECTRICAL PRECIPITATOR 3 Sheets-Sheet 1 Filed June 5, 1948 2 3 2 '3 2 1 y w B n g :1 I IL 4 0 rm 5 7 5 7 5 7 5 7 5 7 5 X A 0 m Z W 5 m E G M Z n a M r u 0 1 N w I E T Q A V E r TUBE C ONDUC TS INVENTOI? GLENN E. ANDREWS BY 0? ATTORNEY o N m on s mlklLovous+ y 1952 e. E. ANDREWS 2,598,337

ELECTRICAL PRECIPITATOR Filed June 5, 1948 v 3 Sheets-Sheet 2 TUBE CONDUC TS ION/Z512 1 2 INVEN7OR GLENN E. ANDRE ws Byu AT RNEV y 1952 e. E. ANDREWS ELECTRICAL PRECIPITATOR 3 Sheets-Sheet 3 Filed June 5, 1948 ero Ax/s Ground TIME TUBE CONDUCTS o 24 6 8 m 2 a m53 Patented May 27, 1952 ELECTRICAL PRECIPITATOR Glenn E. Andrews, Waltham, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass, a corporation of Delaware Application June 5, 1948, Serial No. 31,275

20 Claims.

This invention relates to electrical precipitators for separating dust and smoke from atmospheric air, flue gases and the like, and more particularly to a circuit for energizing such precipitators.

In precipitators of the type to which the invention relates,.the air or other gas to be cleaned is first ionized in a suitable ionizing device, from whence it flows through a suitable precipitating means, where dust and other impurities are separated. The ionizing device comprises at least one pair of ionizing electrodes adapted to have a sufiicient potential placed therebetween to ionize the air that passes therebetween. The precipitating means commonly comprises a plurality of spaced, parallel collector plates of substantial area between which the ionized air flows and on which the dust particles and other impurities are collected due to a difference in potential maintained between adjacent plates. The potential across adjacent plates may be on the order of six kilovolts, while the ionizing potential is substantially higher, for example, on the order of 12 kilovolts or more.

In precipitator power supplies of the prior art which employ voltage doubler circuits, a typical example of which is disclosed in the copending MacKenzie application, Ser. No. 692,893, filed August 24, 1946, now Patent 2,476,247, dated July 12, 1949, two capacitances, two discharge resistors, and two rectifier tubes are required, even though one of the two capacitances may be provided by the inherent capacitance of the collector plates. Also, since the filaments of the two rectifier tubes operate at different potentials, two filament windings must be prgyided on the input or supply transformer.

An object of this invention is to devise a precipitator power supply employing a voltage doubler circuit which requires fewer parts than conventional or prior art power supplies, and yet at the same time does not cause a reduction in the cleaning efficiency of a precipitator using the power supply of this invention.

Another object is to provide a precipitator power supply employing a voltage doubler circuit in which, as compared to prior circuits, one capacitance, one discharge resistor, one rectifier tube, and one filament winding are eliminated without reducing the precipitator cleaning efiiciency, thereby reducing the cost of such power supply.

A further object is to decrease the production of ozone by the ionizing device of a precipitator without decreasing the cleaning efficiency of the 2 precipitator of which such ionizing device constitutes a part.

A still further object is to devise a novel precipitator power supply wherein a pulsating direct potential is applied to the precipitator'ionizing device.

An additional object is to provide an inexpensive precipitator power supply.

The foregoing and other objects of the invention will be best understood from the following description of some exemplifications thereof, reference being had to the accompanying drawings, wherein:

Fig. 1 is a schematic representation of an electrical precipitator together with a supply circuit therefor;

Fig. 2 is a set of curves helping to explain the operation of the circuit of Fig. 1;

Fig. 3 is a diagrammatic representation of a modified precipitator power supply;

Fig. 4 is a set of curves helping to explain the operation of the circuit of Fig. 3;

Fig. 5 is a diagrammatic representation of another precipitator supply according to the invention; and

Fig. 6 is a set of curves helping to explain the operation of the circuit of Fig. 5.

Referring to Fig. 1, reference numeral I indicates generally an ionizing device of an electrical precipitator comprising a plurality of tubular electrodes 2 and a plurality of spaced, parallel fine wire electrodes 3, one between each two successive adjacent tubular electrodes 2, and between which tubular electrodes and fine wire electrodes an ionizing discharge is adapted to take place.

Adjacent the ionizing device I is a precipitating device or collector cell 4 comprising a plurality of collector plates having extensive parallel surfaces and comprising a plurality of ground plates 5 connected to a common grounded lead 6 and a plurality of intervening charged plates '5 connected to a common lead 8.

In order to supply suitable potentials between the ionizing electrodes 2 and 3 of the ionizing device I and a substantially lower potential between the charged plates 1 and the ground plates -5 of the precipitating means l; a transformer 9 is provided having a primary winding NJ, the terminals of which are connected across a suitable source of alternating current through a series switch H, and two secondary windings l2 and I3. One terminal of winding [2 is connected to the common terminal B of the fine wire electrodes 3 of the ionizing device I, while the opposite terminal of winding I2 is connected to grounded lead 5 and the ground plates 5 of collector cell 4.

Opposite terminals of filament winding it are connected to opposite ends of the filament H; of a half-wave rectifier E5, in order to supply heating current to said filament. Rectifier :5 may, for example, be a vacuum tube of the type known as 3324. To complete connections to the cathode 14 of rectifier [5, one terminal of winding is is connected to the ungrounded end of winding i2. Anode it of rectifier i5 is connected to common lead 8 of the charged plates '5 of the precipitating device 4 and also to common terminal A of the tubular electrodes 2 of the ionizing device I. discharge resistor I? having a high resistance, on the order of 300 megohms, for example, is connected between anode l6 and ground. There is an inherent capacitance between the opposed plates 5 and I of collector cell l, and this capacitance is connected across resistor 47 by means of leads 6 and 8.

Now referring to Fig. 2, solid line curve EA represents the potential of terminal or point A with respect to the zero axis or ground, while dashed line curve EB represents the potential of terminal or point B with respect to the zero axis. EB traces a substantially sinusoidal path of six kilovolts peak value when switch ii is closed, since the potential of point B with respect to ground is the voltage across secondary winding [2 of supply transformer 9. When switch l l is closed to energize the circuit, during the first half-cycle when point B goes negative, rectifier It begins to conduct, since point B is connected to cathode id, and charging current flows through condenser l and rectifier iii, charging condenser 4 to substantially the peak voltage appearing across winding 52, which may be six kilovolts, plates 1 (point A) being charged nega- 1 tively with respect to plates 5 or ground. Whenever tube i5 conducts, point B has the same potential as anode it or point A. When the sinusoidal voltage EB reaches its negative peak and begins to go in the positive direction, rectifier I5 ceases to conduct because EB no longer overcomes the opposing voltage EA across condenser 4, rectifier i5 remaining oil and the charge on condenser 4 leaking oii very slowly through resistor ll until an instant in the next negative half-cycle of supply voltage EB is reached at which EB becomes equal to EA, at which instant rectifier I5 again begins to conduct to restore the charge which has leaked ofi condenser 4 through resistor l1, bringing the potential of point A back up in the negative direction to substantially the full peak voltage of source l2.

During steady-state conditions, the abovedescribed leaking-and-recharging process repeats; if the frequency of the source is 66 cycles, condenser 4 is recharged 60 times per second to substantially the peak voltage of the source. Since the resistor I! has a high value of resistance, the draining-cit of the charge on condenser i takes place quite slowly, this discharge being somewhat exaggerated in slope in Fig. 2 for the sake of clearness. Since this rate of discharge is rather low, and since the discharge tends to take place exponentially with respect to the zero axis or ground, the portion of the curve EA corresponding to the discharge of condenser 4, between the times of conduction of tube i5, is substantially linear as indicated.

The voltage EA with respect to the zero axis or ground is the voltage on collector cell t, and

A re during steady-state conditions, as shown, is substantially constant at six kilovolts direct current, with charged plates 7 negative with respect to ground plates 5. Therefore, the collector cell 4 functions in the conventional manner.

The voltage EA with respect to E1; is the voltage supplied to the ionizing device 1, points A and B being located at opposite electrodes of said ionizer. During steady-state conditions, EA with respect to En varies from zero, while tube i5 is conducting, to approximately 12 kilovolts, when his reaches its positive peak of six kilovolts with respect to ground while EA is held at substantially six kilovolts negative with respect to ground by the-non-conduction of tube i5 and the only extremely slow leaking-oil of the charge on condenser 4, as described above. Thus, the ionizer voltage EA with respect to EB rises to a high value of short duration at the frequency of the supply voltage, which in the example given means 60 times per second. At these voltage peaks on the ionizer, point B and fine wire electrodes 3 are positive with respect to point A and tubular electrodes 2. The ionizer voltage Eric is therefore a pulsating direct voltage, with the fine wire electrodes 3 positive with respect to the tubular electrodes 2.

When EAB is approximately 12 kilovolts, ionization of the air molecules occurs. It may be seen that this occurs during short time intervals or in bursts repeated at a rate of 60 times per second, since EAB reaches the ionizing potential only in the vicinity of the positive peaks of En. However, it has been found that this non-continuous ionization or ionization in bursts does not decrease the cleaning eiliciency of the precipitator, but in tact increases it slightly. With an airstream velocity of 300 feet per minute, or five feet per second, a particle in the air stream nioves about one inch in the direction of air flow between pulses of ionizing voltage, which occur at intervals of approximately as, second. In this case, a dirt particle can be a maximum of onelialf inch away from the plane of the ionizing wire at the occurrence of succeeding ionizing pulses or bursts. The existence of this maximum condition does not appreciably interfere with eificient ionization, because under ordinary conditions some ionization of particles occurs when such particles are [2-inch away from the plane of the ionizing wire, and particularly because such particles are subjected to ionization when they are on each of the two opposite sides of such plane.

Another characteristic of the ionizing means, perhaps more important than that just discussed, which keeps the ionizer operating efiiciently even when operating in bursts as in this invention, is the fact that the ions produced by ionization of the gas molecules diffuse in all directions, transversely of the airstream as well as upstream and downstream thereof, and moreover move very far in /60 sec., compared to the distance traveled by the dust particles in the same time. Therefore, the ions travel throughout very large volumes of gas during each of the bursts of ionization, thus producing substantially continuous and complete ionization of the dust particles in the gas by addition to such particles, even though the gas moves between bursts; the dust particles are charged positively in the ionizer if the fine wire electrodes are positive with respect to the tubular electrodes.

In addition, though the production of ions from the gas molecules is not continuous but 5 1 takes place during pulses of short duration ata rate of 60 times per second, the ionsproduced during each burst, if they are not removed from the area of action by effective combination or otherwise, wander around haphazardly in said area between bursts because of the substantially field-free condition existing between such bursts. During this haphazard or random wandering, ionization of some dust particles may take place, even between ionization bursts, thus helping to insure uniform and complete ionization of all the dust particles. Moreover, even if ionization does not ocur in this manner between bursts, beneficial action still results. Because of the large number of ions produced during each burst and because of their wanderings between bursts, just prior to each such burst they are dispersed throughout large volumes of the gas, so that when an electrostatic field is applied between the opposite ionizing electrodes at the beginning of a burst, the ions are already in existence and immediately begin to move toward one or the other of the I opposite ionizing electrodes through a large volume of the gas, colliding with and ionizing dust particles on the way, without the necessity of a relatively long time elapsing from the beginning of the burst before sufiicient ions can be produced and dispersed through the gas.

It has'been found that the above-described effects act, either alone or in combination, to producesubstantially continuous and complete ionization of the dust particles entrained in the air stream passing through the ionizer of this invention, even though the ionizer is supplied with pulsating direct voltage and ionization of the air molecules occurs only in short bursts at a periodicity of approximately second. The cleaning efliciency of a precipitator using the power supply of this invention has been measured as 85 per cent. by the so-called blackness test.

Due to the fact that ionization occurs only in bursts, there is less ionizing time with this invention than with the continuous ionization of prior devices. This means that less ozone is produced by the ionizing means of this invention, a

result which is very desirable. Also, if desired, it

is possible with this invention to increase the peak voltage, and therefore the ionization, without increasing thetotal ozone production over that of the prior devices. If the peak voltage is increased, the ozone production is increased also. However, with the present invention ozone is produced only in bursts and not continuously, so that the total or integrated" ozone can be held down to a value not greater than that produced by prior devices, while at the same time increasing the ionization over such devices.

From the above description, it may be seen that a precipitator power supply has been devised which does not cause a reduction in the cleaning efiiciency of a precipitator using such supply. Such a power supply acts in effect as a voltage doubler circuit, and yet requires only-one capacitance, one discharge resistor, one rectifier tube, and one filament winding on the input transformer, as compared to two of each of these elements required by conventional circuits.

The circuit of Fig. 1 has been found particularly useful for electrical precipitators of the type designed for home or room use. Fig. 3 disclosed a modified circuit which is useful for precipitators of the type designed for industrial use, in which the tubular electrodes 2 of the ionizer I are grounded. In Fig. 3, elements the same as grounded at I8. As before, ground plates 5 of the collector cell 4 are connected together by lead 6, but now lead 6 is connected to ground I8 and the anode I6. Charged plates 1 of the collector cell 4 are connected to a common lead- 8 which is connected to terminal or point C at one end of secondary winding I2, dischargeresistor I I being connected between anode I5 and this.

same end of winding .I2, .or directly across. the

condenser 4. Fine wire electrodes 3 of the ionizer I are connected to terminal or point D at the end ofwinding I2 opposite to terminalC. As in Fig. 1, filament winding I3 is connected to the upper end D of winding I2 and also across filament I4 of rectifier I5.

The operation of the circuit of Fig. 3 will be understood from an examination oi Fig. 4. In Fig. 4, the solid line curve Ec represents the potential of point C with respect to the zero axis or ground, while the dashed line curve E represents the potential of point D with respect to ground. If the potential of point C were taken as a zero axis of reference, En would be sinusoidal about such an axis with a peak voltage of 6 kilovolts, since the voltage E with respect to E0 is the voltage across winding I2.

When switch I I is closed, during the first halfcycle when point C goes positive with respect to point D or cathode I4, or when point D goes negative with respect to point C, rectifier I5 begins to conduct, and charging current flows through condenser 4 and rectifier I5, charging condenser 4 to substantially the peak voltage appearing across winding l2, which may be 6 kilovolts, plate I (point C) being charged positively with respect to plate 5 or ground. During this time of conduction of tube I5, and whenever said tube conducts, the potential of point D has the same value as anode l6, which is zero or ground in this case.

.When the sinusoidal voltage represented .by the initial rising portion of curve Ec reaches its posi-,

tive peak, or when En reaches its negative peak with respect to E0 and begins to go in the posi- E0 across condenser 4. Rectifier I5remains oil and the charge on condensers leaks off very slowly through resistor I1 until an instant in the next negative half-cycle of the swing of point .D with respect to point C is reached at which Ec with respect to ED becomes equal to Ec, at which instant rectifier I5 again begins to conduct to restore the charge which has leaked ofi condenser 4 through resistor I'I, bringing the potential of point C back up to substantially the full peak voltage of source I2. When tube I5 again conducts as described, the potential of point D again drops to that of anode I6 or zero. Between times of conduction of tube I5, En varies as illustrated,

sinceEn with respect to E0 is a sinusoidal wave of 6 kilovolts peak amplitude.

During steady-state conditions, the abovedescribed leaking-and-recharging process repeats; condenser 4 is recharged 60 times per sec-'- ond to substantially the peak voltage of the source. Again, as in Fig. 1, the portion of curve Ec corresponding to the discharge of condenser- 4, between the times of conduction of tube l5, j

is substantially linear asillustrated.

ThevoltageEc with respect to the zero axis or ground is the voltage on collector cell 4, andduringsteadyestateconditions,:.as shown, is substantially constant at six kilovolts direct current, with charged .plate' 1 positive with respect to ground I ground is the voltage applied'to ionizer I. During steadyestateconditions, En varies from zero; while tube' 15 is conducting,.to'approxilmately l2 kilovolts," when Eoreachesits positive peak of six kilovoltsiwith respect to E0 'whileiEc is held at substantially six .kilovolts positive with respect to ground by the non-conduction of tube l 5 and the only extremely slow leaking-ofifof the charge on condenser 4', as described above. Thus, as in Fig. 1, the ionizer voltage En rise'sto a high value of short duration at the frequency otthe supply voltage, or 60 times per-second At these voltage peaks ontheionizer, point D and fine wire electrodes 3 are positive with respect to ground and tubular electrodes 2. The ionizer voltage En is thereforeapulsat-ing direct. voltage, withthe fine wire electrodes 3 positive with respect to the tubular electrodes 2.

As inFig. l, ionization occurs in bursts repeated'atarate of 60 times persecond, since En reaches ionizing potential only in the vicinity of positive peaks of En. However, as previously extifier 15, which is grounded at I9 Ground plates 5 ofcollector cell c are connected together by lead 6', which is connected to ground l9 and cathode l4. Charged-plates 1 of the collector cell 4 are'connected to common lead 8 which is connected to terminal or point F at the lower end of secondary'winding l2, dischargeresistor i'? being connected between cathode Id and this same end of winding l2, or directly across thecondenser 4. Fine wire electrodes 3 ofionizeri are connected to terminal or point G at the upper end of winding l2,-orat the end thereof opposite to terminal F. Filament winding [3 is connected across filament It of the rectifier [5, while anode l6- of said rectifier is connected to the upper end G of winding l2.

It can be seen that the filament hi in Fig. 5

is at ground potential: This is in sharp contrast to the Fig. 1 embodiment, in which the filament point-B goes to a peak of approximately six kilovolts onboth sides of ground, and also to the Fig. 3 embodimentgin which the filament point D goes to a peak of approximately 12 kilovolts with respect to ground. Since the filament Hi in Fig. 5 is at ground potential, it is very much simpler to insulate the filament winding 53 in this embodiment than in the embodiments .of Figs. 1 and 3, in which latter embodiments the filamentwinding must :be insulated in such a way as-to withstand rather high voltages with respect to ground. Thus, a=deci ded advantage is pro-.

8 vided by the Fig. 5 embodiment. Forthls embodimena it is possible to-use a tap on the-primary winding ID to supply the filament l4,rather than a separate filament winding, if desired since' the filament l4 operates at ground-potential and since it is possible to ground'one-side of the primary winding.-

The operation of the circuit of. Fig. 5' will be:

understoodfrom an examination ofFig.-. 6. In Fig. 6, the solid line curve Er represents the potential of point F with respect to thezero axis or ground, while the dashed line curve E'orepre sents the potential of point G with respect to.

ground. Similarly to Fig. 4, if the potential of point F were taken as a zero axis of: reference, Ea would be sinusoidal about such an axis with a peak voltage of six kilovolts, since the voltage;

Ea with respect to EF is the voltage across winding 12.-

From a comparison-of Figs. 3 and-5,.it may be seen that these circuitsare exactly the same with a single exception, which is that the rectifier I5 is poled oppositely inthe-two circuits. Therefore, when'switch H in Fig. 5 is closedto energize-the circuit, voltage variations of a charac ter exactly similar to those described-in connection with Fig. 4 take place, so that the curvesof Fig. 6 resemble those of Fig. l; however, since the rectifier is poled oppositely in Fig.. 5 with respect tonFig. 3, the curves of Fig. 6 are disposed oppositely from the zero axis; with respect to the curves of Fig. 4. Thus, in Fig. 5,*the rec tifier connections are'such that when rectifier l5 conducts to charge condenser 4,-EF- goes neg ative with respect to ground, and the charge on said condenser leaks ofi slightly through resistor ii betweenthe periods of conduction of tube l5. Since the zero line Er for the sinusoidal input voltage (Es with respect to EF) is thus negative with'respect to ground, Es has the shape shown in Fig. 6 and is a pulsating direct voltage which is negative with respect to ground; Es with respect toEr'is a sinusoidal wave of six kilovolts peak amplitude, the input voltage across wind ing [2. The leakingeand-recharging process repeats, and-condenser 4 isrecharged GO'times persecond to substantially ,the peak voltage of the source. 7

The voltage Er with respect to .the zero axis or ground is the voltage on collector cell 4, and.

during steady- -state conditions, as shown, is ,substantially constant at six kilovolts direct current, with charged plate 1 negative with respect to ground plate 5. Therefore, collector cell 4 functions'inthe conventional manner.

The voltage Ec with respect to the zeroaxis or ground is-the voltage applied to ionizer l. During steady-state conditions, Es varies from.

zero, while tube iii is conducting, to approximately 12 kilovolts, when Es reaches its negative peak of six kilovolt-s with respect to EF- while Er is held at substantially six kilovoltsnegative with respect to ground by the nonconduction of tube.

5 and the only extremely slow leaking-on of the charge on condenser l, as described in connection- The ionizer voltage Ed is therefore a pulsatingv direct voltage, with the fine wire electrodes 3 neg-.- ative with'respect to the tubular electrodes 2.

As in theembodiments previously described,

ionization occurs in bursts repeated at a rate of 60 times per second, since EG reaches ionizing potential only in the vicinity of negative peaks of Ed. However, as previously explained, this non-continuous ionization orionization. in

bursts does not decrease the cleaning efiiciency v of theprecipitator.

, Since in Fig. 5 the ionizer voltage (the voltage on the fine wire electrodes with respect to that on the tubular electrodes) is negative, negative ionization takes place, or in other words, the dust particles are charged negatively. Negative ionization ordinarily produces more ozonev than positive ionization. However, it is ossible to get adequate ionization at somewhat lower Volta es than those described in connection with Figs. 1

and 3, so that the ozone generation may be kept down in Fig. 5 to a value not appreciably in excess of that produced by positive ionization. Thus, in Fig. 5 also, the advantage of fewer circuit elements with undiminished precipitator cleaning efilciency is obtained, as in Figs. 1 and 3, without any noticeable undesirable effects.

In Fig. 5, as in Fig. 3, the tubular elements of the ionizer are grounded, which is particularly desirable for industrial units.

Of course, it is to be understood that this invention is not limited to the particular details as described above, as many equivalents will suggest themselves to those skilled in the art. For

example, instead of the commercial SS-cycle a1- ternating current input mentioned, the circuit could if desired be modified to operate at a higher frequency as a radio-frequency power supply, by

supplying the primary winding of the input 1 transformer from a radio-frequency oscillator. In this case, an air-core input transformer would preferably be used. The circuit connections and operation would otherwise be exactly similar to those described above. Also, in the circuit of Fig. l the rectifier could be oppositely poled if desired, in which case, the operation would be represented by curves of the shape shown in Fig. 2 but reversed with respect to the zero axis. Various other variations will suggest themselves. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of this invention within the art.

What is claimed is:

1. An electrical precipitator for purifying gas comprising a plurality of ionizing electrodes between which an ionizing discharge is adapted to occur, a plurality of spaced, parallel collector plates comprising alternate charged and ground plates upon which impurities in said gas are collected, a source of alternating current, a rectifier and filter circuit connected to said source for deriving from said source a substantially constant potential different from ground for energizing said charged plates, and means for applying to said electrodes to energize the same a pulsating unidirectional potential derived from said firstnamed potential and said source, said last-named potential varying between zero and a peak of substantially twice the value of said first-named potential.

2. An electrical precipitator for purifying gas comprising a plurality of ionizing electrodes between which an ionizing discharge is adapted to occur, a plurality of spaced, parallel collector plates comprising alternate charged and ground plates upon which impurities in said gas are collected, a source of alternating current, circuit means including a rectifier and the capacitance inherent in said plates energized by said source -10 and connected to said charged plates, and means for applying to said electrodes to energize the samea pulsating unidirectional potential derived from said first-named potential and said source, said last-named potential varying between zero and a peak of substanially twice the value of said first-named potential..

3. An electrical precipitator for purifying gas comprising at least two ionizing electrodes of opposite polarity between which an ionizing discharge is adapted to occur, a plurality of spaced, parallel collector plates comprising alternate charged and ground plates upon which impurities in said gas are collected, a source of alternating current, circuitmeans including the capacitance inherent in said plates for deriving from said source a substantially constant potential of a predetermined polarity relative to ground for energizing said charged plates, means for applying to one of said electrodes to energize the same a pulsating unidirectional potential derived'from said first-named potential and said source,- said last-named potential varying with respect to ground between said first-named potential and a potential substantially equal to the absolute value of said first-named potential but of a polarity opposite to said predetermined polarity, and means connecting the other of said electrodes to said charged plates.

4. An electrical precipitator forpurifying gas comprising at least two ionizing electrodes of opposite polarity between which an ionizing discharge is adapted to occur, a plurality of spaced, parallel collector plates comprising alternate charged and ground plates upon which impurities in said gas'are collected, a source of alternating current, circuit means including the capacitance inherent in said plates for deriving from said-source a substantially constant potential of a predetermined polarity relative to ground for energizing said charged plates, means for applying to one of said electrodes to energize the same a pulsating unidirectional potential derived from said first-named potential and said source, said last-named potential varying with respect to ground between zero and a potential substantially equal to twice the absolute value of said first-named potential and of said predetermined polarity, and means connecting the other of said electrodes to ground.

5. An electrical precipitator for purifying gas comprising at least two ionizing electrodes of opposite polarity between which an ionizing discharge is adapted to occur, one of said electrodes being a fine wire and the other of said electrodes being a tubular metallic member, a plurality of spaced, parallel collector plates comprising alternate charged and ground plates upon which impurities in said gas are collected, a source of alternating current, circuit means including the capacitance inherent in said plates for deriving from said source a substantially constant potential different from ground for energizing said charged plates, and means for applying between said two electrodes to energize the same a pulsating unidirectional potential derived from said first-named potential and said source, said lastnamed potential varying between zero and a peak of substantially twice the value of said firstnamed potential.

11 being a tubular metallic member, 'aplurali'ty of spaced parallel collector plates comprising altern ate charged and. ground plates upon which im- 'purities'in said gas iare collected, a source of alternating currenhcircuit means including the capacitance inherent in said platesifor deriving .from saidxfirst-namedpotential and said source,

said'last-n'amed potential-varying with respect to ground between said first-'named'po'tential and a potential substantially equalto the absolute value oi. said first-named potential but of ajpolarity opposite to" said predetermined polarity, and means "connecting said tubular electrode to said charged plates.

'LAn electricalprecipitator for purifying gas comprising at least two ionizing electrodes of opposite fpolarity between which 1 an ionizing discharge is adapted to occur,'one of said electrodes being .a'fine wire and the other of said electrodes being a tubular metallic member, a plurality of spaced, parallel collector plates comprising alternate charged and ground platesiupon which impurities in said gas arecollected, a source of alternating current, circuit means including the capacitance inherent in said plates for deriving from said source a substantially constant potential'ofa predetermined polarityrelative to ground for energizing'said charged plates, means for applying to said "fine wire electrode toenergize the same'apulsating unidirectional potential derived 'from'saidfirst-named potential and said source, said last named potential varying with respect to ground betweenzero and a'p'otential substantially equal 'to-twice the absolute value lof'said firstnamed potential and of said predetermined polarity; 'andmeans connecting said tubular electrode to ground.

-8. An electrical precipitator for purifying gas comprising at least two ionizing electrodes of opposite polarity between which an ionizing discharge is adapted to occur, a plurality of spaced,

, parallelcollector plates uponwhich impurities in said gas are collected, said plates comprising a group of charged plates alternating with a group of ground plates, a source of alternating current, means connecting the inherent capacitance between said charged and ground plates in series with a one-way conducting device across said source, whereby said capacitance is charged from said source through. said device, means connecting-one of said electrodes to one terminal of said source, and means connecting the other of said electrodes to one of said groups ofplates.

9. An electrical precipitator'for purifying gas comprising at least two ionizing electrodes of opposite polarity between which an ionizing discharge is-adapted to occur, a plurality of spaced, parallel collector plates upon which impurities in said gas are collected, said plates comprising a group of charged plates alternating with a group of ground plates, a source of alternating current, means connecting the inherent capacitance between .said charged and ground plates in series with a one-way conducting device across said r'source; whereby said capacitanceis charged from said source through said device, a discharge res'istor connected between said two groups of plates, means connecting one of said electrodes to one terminal of said source, and means connect- .12 ing the other of said electrodes "to one ot-said groups of plates.

10. An electrical precipitator for'purifyings gas comprising at least two ionizing electrodes of opposite polarity between which an ionizing discharge is adaptedto occur, a plurality of spaced. parallel collector plates upon which impurities in said gas are collected, said plates comprising a group of charged plates alternating with a group of "ground plates, a'source of alternating current, means connecting the inherentcapacitance between said charged and ground plates in series with a one-way conducting deviceacross said source, whereby said capacitance is charged from said source through said device, means-connecting one of said electrodes'to'said sourcepand means connecting the other oisaid electrodes to one of said groups'of plates and said device.

11. An electrical preci-pitator for purifying gas comprising at least two ionizing electrodes of opposite polarity between which an ionizing discharge is adapted to occur, one of said electrodes being a fine wire and the other of said electrodes being a tubular metallic'member, a plurality of spaced, parallel'collector'plates upon which impurities in said gas are collected, said plates comprising a group of charged plates alternating with a group of ground plates, a source of alternating current, means connecting the inherent capacitance between said charged andground plates in series with a one-way conducting device across said source, whereby-said capacitance is charged from said source through said device, means connecting said wire electrode to oneterminal of said source,'and' means connecting said tubular-electrode to one of said groups ofplates.

12. An electrical'precipitator for purifyinggas comprising at least two ionizing electrodes-of 0pposite polaritybetween which an ionizing discharge .is adapted to occur, one of said electrodes being a fine wire and the other of said'electrodes being a tubular metallic member, a plurality of spaced, parallel collector plates upon which impurities in said gas are collected,-said plates comprising a group of charged plates alternating with a group of ground plates, a source of alternating current, means connecting'the inherent capacitance between said charged and ground plates in series with a one way conducting device across'said-sourceywhereby said capacitance is charged from said source. through-said device, a discharge resistor connected between said two groups of plates, means connecting said wire electrode to oneterminal ofsaid source, and means connecting said'tubu'lar electrode tonne of said groups of platesand said device.

13. An electrical precipitator for purifying gas comprising at least two ionizing electrodes of opposite polarity between which" an ionizing discharge is-adapted to-occur, a plurality of spaced, parallel collector plates upon which impurities in said gas are-collected, said plates comprising a group of charged plates alternating with a group of ground plates, a source of alternating current, means connecting the inherent-capacitance between said charged and ground plates in series witha diode rectifier-across said source. whereby said capacitance is charged from said source through said rectlfier,-means connecting one of said electrodes to one terminal ofsaid source and the cathode of said rectifier, and means connecting the other o'i said electrodes to the group of charged plates and the anode of said rectifier.

14. An electrical'precipitator 'for purifying gas tance between said charged and ground plates in series with a diode rectifier across said source, whereby said capacitance is charged from said source through said rectifier, means connecting one of said'electrodes to one terminal of said source and the cathode of said rectifier, and means connecting the other of said electrodes to the group of ground plates and the anode of said rectifier.

15. An electrical precipitator for purifying gas comprising at least two ionizing electrodes of opposite polarity between which an ionizing discharge is adapted to occur, a plurality of spaced, parallel collector plates upon which impurities in said gas are collected, said plates comprising a group of charged plates alternating with a group of ground plates, a source of alternating current, means connecting the inherent capacitance between said charged and ground plates in series with a diode rectifier across said source, whereby said capacitance is charged from said source through said rectifier, means connecting one of said electrodes to one terminal of said source and the anode of said rectifier, and means connecting the other of said electrodes to the group of ground plates and the cathode of said rectifier.

16. An electrical precipitator for purifying gas comprising at least two ionizing electrodes of opposite polarity between which an ionizing discharge is adapted to occur, one of said electrodes being a fine wire and the other of said electrodes being a tubular metallic member, a plurality of spaced, parallel collector plates upon which impurities in the gas are collected, said plates comprising a group of charged plates alternating with a group of ground plates, a source of alternating current, means connecting the inherent capacitance between said charged and ground plates in series with a diode rectifier across said source, whereby said capacitance is charged from said source through said rectifier, a discharge resistor connected between said two groups of plates, means connecting said wire electrode to one terminal of said source and the cathode of said rectifier, and means connecting said tubular electrode to the group of charged plates and the anode of said rectifier.

17. An electrical precipitator for purifying gas comprising at least two ionizing electrodes of opposite polarity between which an ionizing discharge is adapted to occur, one of said electrodes being a fine wire and the other of said electrodes being a tubular metallic member, a plurality of spaced, parallel collector plates upon which impurities in said gas are collected, said plates comprising a group of charged plates alternating with a group of ground plates, a source of alternating current, means connecting the inherent capacitance between said charged and ground plates in series with a diode rectifier across said source, whereby said capacitance is charged from said source through said rectifier, a discharge resistor connected between said two groups of plates, means connecting said wire electrode to one terminal of said source and the cathode of said rectifier, and means connecting said tubular electrode to the group of ground plates and the anode of said rectifier.

18. An electrical precipitator for purifying gas comprising at least two ionizing electrodes of opposite polarity between which an ionizing discharge is adapted to occur, one of said electrodes 7 being a fine wire and the other of said electrodes being a tubular metallic member, a plurality of spaced, parallel collector plates upon which impurities in said gas are collected, said plates comprising a group of charged plates alternating with a group of ground plates, a source of alternating current, means connecting the inherent capacitance between said charged and ground plates in series with a diode rectifier across said source, whereby said capacitance is charged from said source through said rectifier, a discharge resistor connected between said two groups of plates,

means connecting said wire electrode to one terminal of said source and the anode of said rectifier, and means connecting said tubular electrode to the group of ground plates and the cathode of said rectifier.

19. An electrical precipitator comprising a first collector plate, a second collector plate spaced from said first collector plate, means for producing a unidirectional voltage connected across said plates, a first ionizing electrode, a second ionizing electrode, and a circuit connecting said means and a source of alternating potential in series across said ionizing electrodes.

20. An electrical precipitator comprising a first collector plate, a second collector plate spaced from said first collector plate, a source of unidirectional voltage connected across said plates, a first ionizing electrode, a second ionizing electrode, and a circuit connecting said collector plates and a source of alternating potential in series across said ionizing electrodes.

GLENN E. ANDREWS.

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

UNITED STATES PATENTS Number Name Date 2,000,020 Heinrich May '7, 1935 2,142,128 Hoss et a1 Jan. 3, 1939 2,251,451 Heinrich Aug. 5, 1941 2,469,231 Klemperer May 3, 1949

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