US2318093A - Electrically neutral air cleaning - Google Patents

Description

y 4 N G. PENNEY 2,318,093

ELECTRICALLY NEUTRAL AIR CLEANING Filed June 21, 1940 2 Sheets-Sheet 1 WITNESSES: I [.NVENTOR I Gayiord 1/1/ Pen/76y.

W A BY ATTORNEY y 4, 1943- (5. w. PENNEY 2,318,093

. ELECTRICALLY NEUTRAL; AIR CLEANING Filed Jun 21, 1940 2 Sheets-Sheet 2.

WITNESSES: 'iNVENTOR Gay/0rd 14/ Pannegp Patented May 4, 1943 ELECTRICALLY NEUTRAL AIR CLEANING Gaylord W. Penney, Wilklngsburg, Pa", 'assignor to Westinghouse Electric & Manufacturin Company, East Pittsburgh, Pa, a corporation of Pennsylvania Application June 21, 1940, Serial No. 341,611

21 Claims.

This invention relates generally to electrical precipitators for removing particulate matter such as vapors, fogs, smokes, pollen, dirt and the like, hereinafter embracively called dust, from gases, and more particularly relates to removal of dust-particles from air to be breathed which is discharged into an enclosure in the form of a room or the like.

Electrical precipitator units usually operate on the principle of charging the dust-particles in a flowing gas, and separating the charged par-'\ ticles from the gas through the medium of an electrostatic field which causes the charged particles to migrate to a dustcollecting means. The particles may be charged positively in which case positive ionization is utilized for charging the particles, or they may be charged negatively in which case negative ionization is utilized for charging the particles.

Properly designed and operated electrical precipitators are capable of removing the dust particles, both relatively large and relatively minute,

from a. gas, with extremely high efflciency. However, in some installations a maximum or high efiiciency of air cleaning is not required, so that a precipitator designed for somewhat lower efllciency may be provided, or a high efiiciency precipitator may be operated under conditions producing a lowered efiiciency, for reducing the initial or operating costs of the precipitator. In either case, useful and desirable air cleaning is obtained much above that obtainable with mechanical air cleaners. By high efficiency of electrical air cleaning I mean in general, efiiciencies ranging from about 85% and above, as measured by the blackness test, while by lower eihciencies I mean efliciencies of about 85% and below.

It has been found that the walls of enclosures supplied with air cleaned by an electrical precipitator sometimes have a tendency to become dirty. Apparently, a large part of the small amount of dust not removed by the precipitator deposits on the walls instead of settling downwardly, as usual. This dirtying effect cannot be explained entirely by the effects of convection or by thermal dust precipitation. However, it appears that an electric precipitation occurs, this precipitation being due to the charged dust particles blown into the enclosure from the electrical precipitator, which migrate toward and deposit on the Walls. This effect may be explained as follows. The charged particles establish a space charge or field within the enclosure, with a maximum high voltage substantially at the center of th enclosure and a voltage gradient toward the walls which causes the charged dustparticles to travel or drift to the boundaries of the enclosure, so that a greater fraction of the dust is deposited on the walls than would be the case with uncharged particles which would have a tendency to settle on the floor or other low surfaces with horizontal directional components.

This electrical depositing of dust on the walls of an enclosure is negligible where the electrical precipitators are operating at relatively high efiiciencies or the air supplied thereto has small dust concentrations, but may be disturbing if the electrical precipitator is operating at a relatively lower efiiciency, or if the air has a relatively high dust concentration before cleaning. This is because the amount of residual dust discharged from theusual precipitator of relatively high emciency, is a very small fraction of the total dust content, but in the case of a relatively low-emciency precipitator or where the air contains a i large amount of dust originally, the residual dust is of relatively greater amount; and may contain larger dust particles, and may have an appreciable total electrical charge. Since electrical precipitators are generally operated continuously, or at least for the greater part of the time, this electrical depositing effect of dust may be cumulative, and ultimately results in an undeslrable dirtlness of the walls, even though the cleaned air in the enclosure actually contains considerably less dust than ordinary air.

Accordingly, it is a general object of my invention to reduce theelectrical deposition of dust on the walls of a room supplied with air cleaned by electrical precipitators.

It is a further obfect of my invention to provide an electrical precipitator which discharges cleaned air with the residual dust in the air, on the whole, substantially electrically neutral or uncharged, so that there will belittle or no tendency for the creation of a space charge in an enclosure supplied with the air, thereby preventing the manifestation of electrical deposition of dust on the walls.

Representative and preferred methods and structures by which I accomplish the foregoing and other objects of my invention are disclosed in the following description thereof, from which additional objects, features, combinations, and methods will be apparent.

In the drawings: a

Figure 1 is a vertical view, partly in section and partly in elevation, schematically showing an enclosure in the form of a room supplied with air cleaned by.electrica1 precipitators.

Fig. 2 is a curve representing the static voltage distribution in such room along a line through the middle of the room parallel to the floor.

Fig. 3 is aschematic cross-sectional view of a form of electrical precipitator for discharging cleaned air with residual dust particles, which is substantially electrically neutral or balanced.

Fig. 4 is a schematic wiring diagram for the apparatus of Fig. 3.

Fig. 5 is a-schematic cross-sectional view of 9. second form of electrical precipitator for discharging substantially electrically neutral cleaned air.

Fig. 6 is a part sectional view on the line VI-'-VI of Fig. 5. T

The dust-purifying precipitators which I prefer to utilize are of the type described in my Patent 2,129,783 granted September 13, 1938, and assigned to the Westinghouse Electric 8i Manufacturing Company. Such a precipitator comprises an ionizing chamber and a precipitating chamber successively in the gas-flow, a significant feature of the precipitator being that the ionizing wire is of such small diameter and is so disposed withrespect to suitable cooperating electrodes that the utflizable ionization is obtained without the creation of objectionable proportions of ozone or oxides of nitrogen when.

velocity, the efficiency of such precipitators for- ,cleaning air is very high, say 95%, and any dust particles that may not be collected or deposited have such small charges and are so few in numher that no electrical dust depositing effect is ordinarily noticeable on thewalls of an enclosure supplied with air cleaned by the precipitator.

However, such an electrical precipitator can be operated at lower emciency by, for example, increasing the air-flow velocity through it. This will, of course, lower the cost of the operation of the precipitator and decrease the number of them required to clean a given volume of air in a given time, so that there is a demand for lower eillciency precipitators for some pu p ses. There are, of course, other means by which the efliciency of a precipitator might be made relatively low. Whatever may be the reason for the relatively low cleaning efliciency of the precipitator, such a precipitator frequently discharges air which is not electrically neutral, but which contains charged particles charged unilaterally in accordance with the unidirectional ionization which is utilized in the ionizing chamher; and when the air is supplied to a room. a space charge will be established between the walls of the enclosure. A similar effect mighteven be established with a relatively high efllciency precipitation if the air being cleaned has a high dust concentration'so that although a small fraction of the dust is not collected, say 5% with the precipitator operating at 95% effitical walls of the enclosure is designated by the reference character 2 and the opposite vertical wall by the reference character 4. The charged particles permeating the space between the walls of the room establish an electric voltage-gradient which has a maximum approximately half-way between the walls, and gradually decreases as the distance toward the wall becomes less. Y This voltage gradient is superimposed on whatever may be the relative electric potential of the boundary walls of the enclosure, represented by the base line X.

In accordance with one form of my invention, the cleaned air supplied to the enclosifi'e is divided into two parts one of which passes through one precipitator and the other through a second precipitator.

Referring to Fig. 1,- the enclosure or room 8 includes the pair of vertical walls 2 and 4. a ceiling 8 and a floor it. The room is completed by connecting walls between the walls 2 and 4, and may have suitable windows and doors in a customary manner. The air supplied to the room is electrically cleaned by two separate, but similar, cleaning systems. Each system comprises aconduit i2 having an inlet it near the nected to a pipe l6 leading to the intake of a ciency, the small fraction is taken of an amount which is high initially. a

A typical gradient distribution of the space through theprecipitator by a blower 24, can be controlled. Each precipitator discharges the cleaned air into the room through outlets 26.

In the preferred form of my precipitator described in the aforesaid patent, positive ionization is usedin the ionizing chamber. This means that the residual dust particles not removed ,by the precipitator will be positively charged, and will be carried into the enclosure. The precipitator l8 represents such'a precipitator utilizing positive ionization. In accordance with one form of my invention, the charge due to the positively charged particles discharged by the precipitator I8 is balanced with negatively charged particles from the precipitator it which is, therefore, designed to utilize negative ionization, so that the residual dust particles discharged from it will be negatively charged. The negatively charged.

particles coming from the precipitator l8 commingle in the room 8 with the positively charged to charged dust particles, will be created in the room. It is, of course, evident that the two, precipitators must be suitably operated, or their sizes suitably chosen, so that the total positive charge carried by the air discharged by one of them is substantially equal to the total negative charge carried by the air coming from the other.

The embodiment of Fig. 1 actually discharges charged particles into the room 8, but by utilizing separate negative and positive ionization precipitators the charged particles are of opposite sign, therebypreventing the creation of a space charge in the room and consequently eliminating any tendency of dust to deposit on the walls due to electrostatic action.

In the embodiment shown in Fig. 3 a single precipitator is used 'divided into sections or comcharge is shown in Fig. 2 where one of the v r- 7 Pflrtments each W P Substantially n inessence dependent electrical precipitator with an ionizing chamber and a dust-collecting chamber. In this figure a precipitator 35 is provided with a gasiow directing or conduit means through which the air to be cleaned flows, the conduit means {tween tubular ring zone or'chamber comprises a series of infor the precipitator 30. .For

ionizing wires fsulated plates 52. with the plates of the respective series alter- I Bil and a series of grounded plates hating.

Fig.- 4 schematically shows electric connections the section A the 38 are preferably plates 44 with the v he precipitat zone comprising the series of plates 52' and M, which are oppositely charged nondischarging electrodes, the ionized gas particles, which have high mobility, will be quickly deflected to a plate surface and rendered electrically neutral. The charged dust particles will also give up their charges if the plates are long enough, and the voltage between the plates high enough, and the air-velocity such that the charged particle have an opportunity to migrate to the collecting plates. Such a precipitator will, of course, yield high efficiency for dust-collection but in the event that any one of the various factors entering into the operation of a precipitator for high efficiency should be .so adjusted or changed so that the efliciency is decreased, orthe precipitator used for cleaning airwith high dust content, a certain amount of the air-borne dust particles will connected to be at the same potential. the tubular electrodes 40 1 are preferably grounded, and the plates of each of the series of plates 42 and M are conductively connected together with one series insulated relative to the other. Similar electrical relationships 1 are utilized in'the section B.

Referring to Fig. 4, it may be observed that a source of voltage is as a direct current battery having a positive ter-.

, minal at one end and a negative terminal at the 5 other, the battery being provided with suitable 1 means for obtaining desired intermediate voltages.

The center of the battery-source is grounded as indicated at 56, andthe electrodes ill and 48 .and the series of plates 44 and 52 are also grounded, are at the same poand consequently,

The ionizing wires 38 are negative with tential.

respect to the grounded elements and, conse-.

quently, are connected to the battery at a point 1 close to or at the negative terminal. The-ionizing wires 46 are positive with respect to the grounded elements and are, consequently, connected to the battery at a point close to or at the positive terminal. By suitable connections 60 and 62, respectively, the insulated series of pistes '47 'are'irnaintained 'at a --potential with re;

spect to the series of grounded plates 45, and the insulated series of plates 50 are maintained at a potential with respect to theseries of grounded plates 52, for causing matter which has been s'ufliciently charged to migrate to" and deposit on oppositely charged plates. The voltage between the ionizing wires and electrodes of'the ionizing chamber, and the voltage between the 'plates of the dust collectingschamber are preferably ad justablei age 54 as a direct current battery, it is clearly evident that for practical applications, the required voltages would usually be obtained from commercial alternating current sources by suitable transtormers and rectifiers, or similar means.

In the operation of theprecipitator shown in- Fig. 3, the air flow will be such as to pass first through the ionizing chambers and then through the dust-collecting chambers, as indicated by the arrows. The part of the air flowing through the section A will first pass through the negatively ionized ionizing chamber where cles will be negatively charged and some of the gas atoms or molecules similarly negatively ionized. In passing through the dust-collecting indicated schematically at 54 the dust parti- "cipitator residual charged particle flowing out of the section A will be negatively charged while that flowthe outlet notbe precipitated and may in charged condition. However, such the enclosure itself 1 short. l

chamber.

Wl'ii'l''I havesh'own the source of volt- In Fig. 5, I show a further modification of an electrical precipitator in which an ionizing zone or chamber and a precipitating zone or chamber successively in the gas flow are utilized as before. However, an additional ionizing means is placed in the output side of the gas flow to reverse the charge on a fraction of the residually charged particles passing through the dust collecting means.

Referring to Fig. 5, the gas-flow directing or conduit means through which the air flows comprises an electrical precipitator 10 comprising an ionizing chamber 12 having ionizing wires 14 for producing positive static field established with cooperating grounded tubular electrodes 16. The precipitating chamber comprises, as before, means for establishing an electrostatic precipitating field between nondischarging electrodes in the form of a plurality of series of plates in which the plates of one series alternate with those of another. and the respective series are maintained at a relative potential difference for precipitating the particles charged or ionized in the preceding ionizing Disposed after the precipitating chamber, in the direction of gas flow, is a second ionizing means comprising a negatively charged ionizing wire 18 between two insulatedly supported plates 80' and 82 on each side of the wire to provide a secondary ionizing zone 8 the plates paralleling the gas flow and being spaced from the sides of the casing of the precipitator 10 by supporting insulators 85. The plates 80 and 82 are connected to the positive terminal of the potential source applied to the wire 18 so that the field between the wire and the plates will be negatively ionized, preferably in accordance with the teachings of my aforesaid patent, that is, with inappreciable generation of ozone or oxides of nitrogen.

The plates 80 and 82 are preferably of a length in the order of the length of the precipitating plates in the precipitating zone, and the transverse area between them is approximately onehalf the cross-sectional area of the gas flow passage in the precipitator thereat. Accordingly. about one-half the gas or air flowing through flow out of the preif the outlet conduit is too.

ionization in an electroresidual dust will be reversed. At the outlet end the ionizing zone 12 and the subsequent precipitating zone will fiow through the ionizing zone 84 between the wire 18 and plates 88 and 82, while the remainder or the total air will by-pass this additional ionizing zone, flowing through the spaces, between the casing sides and each or the plates 82 and 84.

In the embodiment being described, the first ionizing zone I2 utilizes positive ionization so that any residual dust passing beyond the precipi-' tating chamber will be positively charged. However, half of this dust will passthrough the ionizing zone'84, which utilizes negative ionization so that the charge on this proportion 01 the the precipitator ID the charge due to negative ly charged dust and the charge due to positively charged dust will neutralize each other so that any air supplied to the enclosure will be substantially electrically neutral.

In this form of my invention, I prefer to in- .clude' a grounded plate 86 between the plates 88 and 82, which is disposed after the ionizing wire 18. Thi plate 88 can be conventionally used for supporting the ionizing wire 18 by arms If desired,-screens-80 may be-applied across the forward edges of the plates 80 and 82 in order to more definitely define the field about the ionizing wire 84.

In the operation of the device'shown in Figs. 5 and 6, substantially all of the .gas or air flowing through the precipitator III will first pass through the ionizing chamber utilizing positive ionization,-

where positive gas ions are created, and the dust particles in the gas or air are positively charged. In passing through the precipitating zone the positive gas ions are effectively discharged, and

' positively charged dust collected, the proportion 'of the collected dust to the total dust content de pending upon the cleaning efiiciency or the precipitato'r. Assuming tha't'th'e precipitator is of relatively low efiiciency, the gas or air flowing from the dust collecting chamber will contain moreor-less dustparticles which are positively charged and which are distributed through the gas stream. A part of this gas stream will flow through' the conduit compartm'ent including the ionizing zone 84 where the previously positively charged dust particles have their charges reversed and become negatively charged, and negative gas ions are created if the cleaned gas or air contains an ionizable gas, which is the case with air. This portion of the gas or air will fiow past plate 86 and through the electrostatic field which this plate establishes with the plates 80 and 82. Because of the high mobility of the gas ions, they will be quickly deflected to a plate of opposite sign and become electrically neutral, but the low mobility dust particles will, for the most part, pass through this field without being deposited because of the wide spacing between the electrodes establishing this field. These dust particles have negative charges and will commingle with the positively charged dust particles flowing in the portion oi the gas or air which does not flow through the ionizing zone 84, but flows mostly outside the compartment boundplates and 82 is generally suflicient to 'a means for discharging and so neutr ed by the plates 3t? and 82 which, consequen are also partitions dividing the outer conduit into different air-flow paths. The charged dust particles oi opposite signs will consequently neutralize inthe conduits beyond the plates 80 and 82, or in the enclosure supplied with the gas or air cleaned by the precipitator I0.

A single plate 88 spaced midway between the gas ions. The wide spacing between the plates and their limited length limit the precipitation of the dust by them, so that an ionizing zone 84 of substantially the same characteristics of the ionizing zone 12 can be used. A. device utilizing approximately 12,000 volts direct current between the ionizing wires 14 and the grounded electrodes 18 with a spacing of. 1% inches, and

5,000 volts direct current between the two series 20' of plates or the dust-collecting chamber, the plates being spaced 1'; inch apart, will produce substantially electrically neutral air with a diroot-current voltage between the plate 86 and the plates 80 and 82 of about 12,000 volts, and an air velocity of approximately 325' feet per minute. These figures are given by way of illustration, and are not necessarily limitations since the values given can be varied, and preferably are varied in accordance with the kind of dust being removed.

Precipitators such as shown in Figs. 3 and 5 are efi'ective under widely varying conditions. Thus,

if the gas velocity is increased considerably the residual charged particles passing out of the precipitating chambers with the gas will be increased in number. However, the relative proportion 01' negatively charged particles and positively charged particles remains the same regardless of the velocity. This enables the precipitators to be operated at any desired efilciency and still prevent the creation of a space charge in the enclosure. The electric deposition of dust on the walls will be prevented by using the apparatus proposed since the total charge due to charged particles is substantially nil, and is insufilcient to establish a space charge in the enclosure.

It should be pointed out that if a space charge exists in the enclosure in which there is a certain amount of dust in the contained air, the total dust deposited on the walls tends to be propor tional to approximately the square of the total amount oi the dust. Furthermore, with relatively low efliciency electrical precipitators, each particle of dust carries a greater charge on the average. Consequently, the dirtying effect on the walls due to electric precipitation which may be negligible at the higher efiiciencies of electric cleaning may be very objectionable with precip itators operating at relatively low efliciencies. By the use of the diil'erent expedients described and shown the space charge within the enclosure is eilectively rduced, and in fact, can be substantially entirely eliminated by building or operating the cleaning system suitably with ionizing and dust-collecting characteristics necessary for the purpose. By so reducing or eliminating the space charge, the possibility of dirtying of the walls by electrical deposition is likewise reduced or eliminated. In general, an adjustment of the ionizing current in the different ionizing zones, or the plate voltages in the dust-collecting zones, or

both, can be utilized in the different embodiments of my invention to control the charge on the residual particles coming out of the zones.

In some cases it might even be desirable to provide difierently apportion the fractions of the-total air passing through the different sections of the precipitators shown in Figs. 3-6 or through each precipitator shown in ,Fig. 1. In such cases the relativeionization should be changed accordingly, that is, the residualv dust discharged with the smaller fraction of air should be more highly charged.

While I have shown my invention in forms which I now believe to be preferred, it is obvious that many modifications may be made, and that the teachings of my invention may be applied to other types of precipitators including that shown and described in the application of Edward H. R. Pegg, Serial No. 286,577, filed July 26, 1939, and assigned to the Westinghouse Electric 8: Manufacturing Company.

I claim as my invention:

1. The method of providing an electricallyneutral discharged gaseous fluid from an electrical precipitator means, which comprises passing the fluid through a unidirectional ionizing zone for charging particles in the fluid with a predetermined polarity, and then passing a fraction only of the fluid through a unidirectional ionizing zone of a polarity opposite to that of the first said polarity.

2. The method of providing an electricallyneutral discharged gaseous fluid from an electrical precipitator means, which comprises passing the fluid through an ionizing zone for charging the dust in the fluid with a predetermined polarity, collecting a large fraction of the charged. dust in the precipitator, subsequently passing a fraction only of the fluid, containing residual dust, through an ionizing zone of a polarity opposite to that of the first said polarity, and combining the said fraction of the fluid with the remaining part of the fluid.

3. An electrical precipitator in which dust is removed from a flowing gaseous fluid, comprising gas-flow directing means for said fluid, said means having a plurality of treating zones; dustcharging and dust-collector means in one of said zones, comprising an ionizing'wire having one pole of a unidirectional electric power source connected thereto, and cooperating electrode means having the opposite poleof said power source connected thereto; and an ionizing wire in another of said zones, having one pole of a unidirectional electric power source connected thereto,

the last said pole being of a polarity opposite to that of the first said pole; said gas-flow directing means having provisions for directing fluid flowing through said one zone so that it does not flow through said other zone.

t. In an electrical precipitator, a grounded casing, a pair of plates, insulating means for insulatedly supporting said plates in substantially uniformly spaced relation opposite each other, an ionizing wire spaced from and between said plates, and screen means across edges of said plates near said wire.

5; The method of electrically cleaning dust from dust-containing air to be supplied to an enclosure, which comprises passing air through an ionized electrostatic field having predetermined ionizing characteristics for ionizing particlesand charging the contained dust in the air-flow; then passing the air through an electrostatic field having spaced oppositely charged boundaries of some extent in the direction of air flow, for precipitating a portion of the charged dust particles and discharging some ionized particles; then passing cleaned air through an ionized fleld of. predetermined characteristics difi'erent from those of the first said ionizing field for counterbalancing the charge of the residual dust flowing through said spaced electrodes, and ionizing particles in the air flow; and then passing the air containing the last said ionized particles through an electrostatic field having spaced oppositely charged boundaries of some extent in the direction of air flow for discharging a portion of the ionized particles. p

6. A gas-cleaning precipitating-apparatus for cleaning dust-containing air, comprising conduit means; ionizer means in said conduit means comprising ionizing electrodes including relatively fine ionizing wires less than 32 mils in diameter. producing a positively ionized electrostatic field, and spaced curved relatively large electrodes between which the said ionizing wires are disposed; a dust-precipitating chamber in said con duit means following said ionizer means,'said dust-precipitating chamber comprising a plurality of relatively closely spaced alternately insulated and uninsulated non-discharging electrodes of some extent in the direction of air-flow and dividing the air into a plurality of distinct layers for collecting dust particles charged by said ionizer means, and for discharging some particles ionized by said ionizer means; separate charge-neutralizing means including an extended ionizing wire in said conduit means, for counterbalancing the charge of any residual charged particles in the cleaned air passing from said precipitating chamber, said charge-neutralizing means being such that air discharged therefrom is substantially free of ionized particles.

7. A gas-cleaning precipitating-apparatus for cleaning dust-containing gas comprising gas-flow directing means having therein: ionizer means having an ionizing electrode for producing ionization current of predetermined characteristics, for charging dust particles in the gas and for ionizing gas particles; means comprising a plurality of spaced, oppositely-charged alternately insulated and uninsulated non-discharging electrodes of some extent in the direction of air flow for precipitating a substantial part of the charged dust particles, said non-discharging electrodes dividing the air flow into a plurality of layers and discharging the ionized gas particles; a

separate ionizer means having an ionizing electrode for producing ionization current of predetermined characteristics difierent from those of the first said ionizer means; and separate means comprising a plurality of widely spaced, oppositely-charged non-discharging electrodes of limited extent in the direction of air flow and following the second said ionizer means for discharging gas particles ionized by the second said ionizer means without appreciable dust precipitation, said widely-spaced electrodes dividing the air flow into a plurality of layers.

said precipitating means including a plurality of closely-spaced alternately insulated and uninsulated non-discharging electrodes of some extent in the direction of fluid-flow, and dividing the fluid-flow into a plurality of layers; said conduit means further including therein a chargeneutralizing means for aflecting the residual charge of the cleaned fluid passing through said precipitating means, said charge-neutralizing means comprising ionizer means for establishing an ionized field oi characteristics diflerent from those of the first said ionizer means, the last said characteristics being such that 'a polarity oi ionization opposite that of the first said polarity predominates, and a plurality of widelyspaced oppositely-charged, non-discharging electrodes of some extent in the fluid flow, following said second ionizer means for discharging gas particles ionized in' said second ionizer means.

9. An electrical precipitator for cleaning a flowing dust-bearing gaseous fluid, comprising conduit means through which the gaseous fluid is adapted to flow, said conduit means having therein: ionizer means for establishing an ionized field of predetermined characteristics through which the gaseous fluid. is adapted to flow, said'characteristics being such that one polarity of ionization predominates; dust-precipitating means following said ionizer means in the direction of fluid flow for precipitating-dust particles charged in said ionizer zone and for neutralizing gas particles ionized in said ionizer zone, said dust-precipitating means including a plurality of spaced alternately insulated and uninsulated non-discharging plate-electrodes of some extent in the direction of fluid-flow, and dividing the fluid-flow into a plurality of layers; a chargeneutralizing means for afiecting the residual charge 01' the cleaned fluid passing through said dust-precipitating means, said charge-neutralizing means comprising ionizer means for estab-- lishing an ionized fleldoi' characteristics different from those of the first said ionizer means, the last said characteristics being such that a polarity of ionization opposite that of the first said polarity predominates, and a. plurality of spaced oppositely-charged, nonj-discharging plate electrodes of some extent in the fluid flow, following said second ionizer means for discharging gas particles ionized in said second ionizer means,

the lastsaid oppositely-charged non-discharging plate electrodes dividing the fluid flow into particles in the air flow, the cleaned air flowing from said air-cleaning means with a residual charge, and means associated with said conduit means and including an extended ionizing wire in said conduit means between said air-cleaning means and said air-outlet, for substantially neutralizing said residual charge, the last said means including gas-ion neutralizing electrodes, whereby the air discharge from said air-outlet is substantially electrically neutral.

11. An electrical precipitator for cleaning a flowing dust-bearing gaseous fluid, comprising conduit means for the flowing gaseous fluid containing a first ionizer means having ionizing electrode-means for establishing an ionized field for charging dust particles in said gaseous fluid flowing through said ionized field with a charge having a predominating polarity, said conduit means including conduit-dividing means for defining a separate fluid-flow compartment in said conduit means, and a second ionizer means in said compartment for charging dust in the gaseous fluid flowing through said compartment with a charge having a predominating polarity opposite to that of the first said polarity.

12. Apparatus for supplying electrically cleaned gas to an enclosure, comprising two difierent electrical precipitators both operating to electrically precipitate ionized particles from a gas, said precipitators having separate outlets for the discharge of cleaned gas therefrom, and means for supplying, to said enclosure, gas discharged from both said outlets whereby said precipitators both supply cleaned gas to said enclosure, both precipitators operating under such conditions that they produce a material quantity of unprecipitated ionized particles along with the cleaned gas, one of said precipitators including a positive ionizing means, and the other including a negative ionizing means, whereby both positively and negatively charged particles are produced by the'two precipitators.

13. A precipitator system comprising a conduit means, said conduit means having therein air-cleaning means for electrically charging and collecting dust particles in the air flow,'said aircleaning means having such a cleaning efficiency for removing dust particles that cleaned air flowing from said air-cleaning means contains dust particles having a residual electrical charge of a certain polarity, and means for causing electrical charges of opposite polarity to be introduced into said cleaned air for counteracting and substantially balancing said residual electrical charge of the dust particles.

14. An electrical precipitator system comprising a gas-flow directing means, partition means in said gas-flow directing means for dividing the gas-flow into a plurality of distinct separated gas-flow paths; distinct means in one of said gasflow paths for electrically charging and precipitating dust particles in the gas-flow therethrough, said distinct means comprising ionizing electrode means for continually producing a first electrostatic field having a predominating ionizing effect of a certain polarity on the dust particles; distinct means in a second of said gas-flow paths, comprising ionizing electrode means for continually producing a second electrostatic field havin a predominating ionizing characteristic of a polarity opposite to the first said polarity,

means for mixing the gases flowing out of said gas-flow paths, and means for controlling the net effect of the first and second electrostatic fields on the residual charge in the mixed gases.

15. The method of supplying electrically cleaned gas to an enclosure, which comprises supplying to said enclosure a first portion of gas which has been passed through a last unidirectionally ionizing field having an ionizing characteristic of a certain polarity, and mixing with said first portion of gas, another portion of gas which has been passed through a last ionizing field having an ionizing characteristic of a predominating polarity opposite to that of the first said polarity.

16. The method of cleaning a. flowing dustbearinggaseous fluid containing an ionizable gaseouscomponent, which comprises causing said fluid to pass through an ionized field of one polarity for electrically charging the contained dust, and ionizing gas particles of said gaseous component, subsequently subjecting the flowing gaseous fluid to the action of an electrostatic,

field established between extended non-discharging electrodes for precipitating most of the charged dust, and discharging the said ionized gas particles by contact with said electrodes, then subjecting cleaned gaseous fluid to the action of a second ionized field for substantially counterbalancing the charge-of residual charged dust which has not been precipitated by said electrodes, and then subjecting this cleaned gaseous fluid which has been subjected to the said second ionized field, to the action of an electrostatic field established between non-discharging electrodes for discharging gas particles ionized in said second ionized field.

17. An electrical precipitator for cleaning flowing dust-bearing air or the like, comprising an ionizer means including spaced relatively insulated electrodes for producing an ionized field, through which a portion of the air passes, said relatively insulated electrodes having a potential source connected thereto for producing positive ionization; a plurality of spaced non-discharging electrodes adapted to be maintained at a difference in potential with respect to each other. between which said portion of air passes in dis tinct strata after passing through said ionizer means; another ionizer means including spaced relatively insulated electrodes between which another portion of the air passes, the lastsaid electrodes having a potential source connected thereto for producing a preponderance of negative ionization; additional spaced non-discharging electrodes adapted to be maintained at a potential with respect to each other, between which the last said portion of the air passes after passing throughthe last said ionizer means; and a. conduit portion for combining the portions of the air passing between the respective non-discharged electrodes, for neutralizing removed from a flowing gaseous fluid, comprising gas flow directing means for said fluid, said means providing a plurality of treating-zones, said gas-flow directing means having a gas inlet and a gas outlet between which said zones are disposed; ionizer means in one of said zones, comprising an ionizing electrode having one pole of a unidirectional electric power source connected thereto, and cooperating electrode means having the opposite pole of said source connected thereto; a dust-collector means in said one zone comprising a plurality of spaced electrodes, said ionizer means and dust-collector means being successively in the path of gasflow; an ionizer means comprising an ionizing electrode in another of said zones, having one pole of a unidirectional electric power source connected to said electrode, the last said pole being of a polarity opposite to that of the first said pole; and electrode means in said other zone comprising a plurality of spaced electrodes at a potential with respect to each other, the two last said means being successively in the path of gas: flow; said gas-flow directing means having provisions for dividing fluid flowing from said gas inlet to said gas outlet so that a fraction of the fluid does not flow through at least one of said zones.

20. An electrical precipitator comprising a conduit means having a gas-inlet and a gas-outlet, an ionizer means and a dust-collector means successively in said conduit means between said gas-inlet and said gas-outlet, said ionizer means comprising an ionizing electrode means for producing ionization of one polarity, said dust-co]- lector means comprising a plurality of relatively closely-spaced, alternately relatively insulated and unins'ulated plates, a second ionizer means comprising an ionizing electrode for producing an ionized field having a predominating ionization of a polarity opposite to that of the first said polarity, and a number of relatively widelyspaced, alternately relatively insulated and uninsulated plates following said second ionizer means, said second ionizerrmeans and the last said widely-spaced plates being in said conduit means before said gas-outlet.

21. A gas-purifying precipitator system for electrically removing dust-particle from a flowing dust-laden gas, comprising conduit means through which the gas flows, said conduit means including therein an electrical precipltator means for electrically cleaning the gas flow to a high degree but permitting a small amount of residual dust-particles to pass, therethrough charged in a predetermined potential, and electrical means for substantially counterbalancing the charge of said residual dust-particles, said electrical means comprising an ionizing wire charged to a polarity opposite to the prevailing charge on said residual particles.

GAYLORD w. PENNEY.

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