CA1137427A - Wet-wall electroinertial air cleaner - Google Patents

Abstract

WET-WALL ELECTROINERTIAL AIR CLEANER
ABSTRACT OF THE DISCLOSURE
An apparatus to efficiently remove dust from air is disclosed. The apparatus comprises in combination an inertial unit and a concentric wire-in-tube precipitator, consisting of a thin charging wire located coaxially in a cylindrical vertical tube whose etched walls are continuously flushed with water. Thus, a continuous stream of dust laden air blown rotationally into the tube is electrostatically charged, and cleaned of the dust particles by depositing them on the wet-wall surface which flushes them out.

Description

37~7 BACKGROUND OF THE INVENTION

FIELD OF THE IN~ENTION:
The instant invention comprises an apparatus for utilizing .both electrostatic forces and inertial forces to effect precipitation of particulates onto a self-cleaning wet-wall scrubber, thereby cleansing dust laden air which is rotationally blown into the apparatus.
DESCRIPTION OF THE PRIOR ART:
Various types of air cleaning devices such as bag collectors, cyclones, electrostatic precipitators, and wet scrubbers have :
demonstrated ability for collecting fine dust such as the :~
inhalable fraction of cotton dust which is smaller than 15 microns. However, the efficiency of cyclones decreases rapidly for particles under 10 microns and high operating pressure is a~
, ~r 11374~7 needed to remove particles finer than 5 microns. Wet scrubbers remove particulates from a gas stream by sweeping the gas with a spray of water droplets or by impinging the dust laden gas against a wetted surface. Simple spray chambers or packed tower scrubbers are inefficient for removal of small size dust. High energy wet scrubbers are needed for high efficiency, and water entrainment from the sprays is a serious problem. In both cyclones and wet scrubbers pressure drops of 3 to lO0 inches of water are needed for high efficiency depending on the particle size to be collected.
Fabric filters used in bag collectors are intrinsically high efficiency collection devices, but fine dust plugs the bags and large pressure drops develop. Bag failure which requires replacement is a considerable cost factor.
Conventional types of electrostatic precipitators provide high collection efficiency for fine particles and have low operating pressure. Single-stage precipitators of conventional ; design are of two types: (1) tubular and (2) pocketed plate.
` These precipitators are designed to achieve efficiencies inthe range of 99 percent with flow velocities in the range of

2 to 10 fps. In most precipitators, the particulate material is collected as a dry cake on the plates or wall of the tube, and the collector is rapped periodically to release the cake which falls into bins. Depending on the electrical nature of the cake, the collected material can affect the charging current, cause arcing, reduce the effective field strength, 1~379~2!7 and produce a conditlon which causes back corona. The net effect i8 that performance of the precipitator ia affected adveraely and the size of the unit must be increased to offset thQ adverse effect of the cake. P~pping to relesse the cake often results in some reintrainment of th~ collected material, and errosion of the cake must be avoided by ~eeping the gas flow rate relatively low. Further, cakes of combustlble materials such as cotton dust constitute a fire hazard in dry types of preclpitators where arcs are likely to occur in the course of r~al operation.
A nominal preclpitator operates at volume flows of 2 to 10 ft per second and if the volume flow i8 increased to the 40 ft per secont range ~ the efficiency wlll fall ln the minal precipitator to appro~lmately the 502 range.
To handle large volu~es of alr, both electrostatic precipitators and bag filters require large collector 6urfaces anc the accumulated layer of combustible materials such as cotton dust constitute a fire hazard in these devices.
Periodic cleaning of the collecting surfaces by rapping or back flushing in temporarily isolatet sections provldes for continuous operatlon, but does not ~ inate the fire hazard.
~et sprays have been combined with electrostatic precipitators to increase the efficiency of collectlng fine dust snd to flush the dust from the collector surfaces; however, water entrain~e~t in the gas ~tream li~its the capacity of this type of unit~nd a relatively large volume of water is needed to remove material from the large plates.

1~37~Z7 SUMMARY AND OBJECTS OF THE INVENTION:
The instant invention is a unique apparatus designed and constructed to achieve high efficiencies of dust removal from air by combining the optimum conditions of feeding air rotationally into a chamber equipped with a device which electrostatically depos$ts the dust onto a wetwall surface which flushes the dust out of the system and exhausts clean air wich may be recycled.
It is the primary object of the invention to remove dust particulate from the air.
It is a second object of the invention to remove dust particulate from the air by means of a unique combination of inertial forces and electrostatic forces in a tubular electrostatic precipitator with a wet flushing device.
It is another object of the invention to introduce the air into the apparatus rotationally.
It is another object of the invention to reduce the amount of water necessary for dust removal.
It is another object of the invention to reduce fire hazards in existing dust removal equipment.
It is another object of the invention to utilize small size equipment and still achieve high efficiency dust removal from high volumes of air.
It is another object of the invention to eliminate the build-up of cake on the walls of dust removal equipment.

~`''' -4-,, .,~, ~3742~

It is another object of the invention to eliminate rapping in electrostatic precipitators.
In accordance with the present teachings, an inertial-electrostatic precipitator system is provided for decontaminating a gas stream which has particles dispersed therein the particles including fines of under 10 microns. The system which is provided comprises a vertically-mounted collector tube having an upper inlet and a lower inlet with means supplying an electrically conductive liquid to the inlet in a full circle thereabout to create downflowing liquid on the inner wall of the tube. An annular catch sump is provided adjacent the outlet to receive the downflow-ing liquid from the tube with means feeding the gas stream stream which has the particles dispersed therein into the inlet at high velocity and for imparting rotational movement to create a centrifugal force inducing at least the particles of over 10 microns to migrate toward the downflowing liquid to be washed down into the sump. The velocity is sufficient to cuase the rotational motion of the gas s~ream to induce spiral flow of the liquid in the downflowing liquid whereby the downflowing liquid uniformly wets the inner wall of the tube. A discharge electrode is provided coaxially disposed within the tube with means to impress a high voltage between the discharge electrode and the downflowing liquid to create an electrostatic field therebetween and to charge the particles dispersed in the gas to further induce the particles including the fines to migrate towards the downflowing liquid thereby substantially fully decontaminating the gas stream. The take-off pipe is inserted in the outlet spaced from the inner wall of the tube carrying the downflowing liquid to form an exhaust for the decontaminated gas stream which is isolated from the downflowing liquid.
The instant invention wet-wall electroinertial unit is a unique application of electrostatic and inertial techniques that provides highly efficient collection of fine dust with high air flow rates at lower operating pressures than now required by cyclones. Furthermore, the fine 1~374Z~7 material is washed off the collector surface continuously, such that it does not affect the operating pressure or electrical field or create a fire hazzard, in a manner that does not produce water droplets that are likely to be entrained and expelled with the cleaned air.
Since the collected material is continuously washed from the walls in the wet-wall inertial unit (instant invention), the unit does not have to be designed or operated at reduced voltages to allow for the cake.
The net result is that high efficiency can be achieved at high flow rates with a unit that is smaller than the conventional single-state precipitator.
Further, since rapping is not needed, this unit can be constructed with much lighter materials than used in units of conventional design.
Although the 3-inch water pressure drop of the wet-wall electroinertial unit at 800 cfm is greater than that of a conventional electrostatic precipitator, it is much less than that of a cyclone with comparable efficiency. The efficiency of the wet-wall electroinertial air cleaner used in the cyclone mode without voltage is about 80 percent on the fine cotton dust at a flow rate of 800 cfm. To achieve 99 percent efficiency ~ -5a-~ J

~3742~

in collecting the fine, low-density cotton dust, operating pressures of 20 to 40 inches of water probably would be necessary in a conventional cyclone.
Single stage precipitators of conventional design have been flushed with water to remove the precipitated material without forming a cake. However, the water flows straight down the wall of the tube. In the instant invention, the rotary movement of the gas flow causes the water to flow in a spiral path which covers the tube better and produces a scrubbing action. As a result, the amount of water needed to flush the instant invention is less than that needed to flush the conventional straight flow units. This can be demonstrated in the instant invention by turning off the air flow. The water then flows straight down the wall and breaks into separate streams which do not flush the entire wall effectively.
BRIEF DESCRIPTION OF THE DRAWINGS:
Figure 1 is a side cross-sectional view of the wet-wall electroinertial unit showing the salient features.
Figure 2 is a top view showing a tangential air spinner.
Figure 3 is a schematic diagram describing a multitude module with vane type air spanners.
Figure 4 is a detail of the clean air exhaust end of the wet wall inertial unit.
Figure 5 is a schematic diagram detailing the means for recycling the cleaned air back to the work area.
DESCRIPTION OF THE PREFERRED EMBODrMENTS:
Referring now to figure 1 wherein particle laden air or some contaminated gas or air is introduced into a :

vertical positioned cylindrical chamber through the inlet end 1. This particle laden or contaminated air or gas is then introduced into an upstream inertial spinner or cyclone 10 which causes it to rotate (figure 2). In the system illustrated, the inertial spinner consists of a transition duct which ends in a flattened cross section and which is connected to the upper cylindrical cap 3 of vertical electroinertial cylinder 6 in an orientation normal to the axis of the body cylinder 6 and tangential to the wall of cylinder 6. Thus cylinder 6 substantially forms a vertical cylinder (figure 1). Air/gas entering the unit tangentially at the upper end acquires a rotating movement. A charging wire 5 is positioned coaxially in the vertically positioned cylindrical 6 and is supported on insulators 2 on both ends of cylinder 6. Charging wire 5 forms a means for imparting an electrical charge to the contamination particles in the flowing air or gases. Wire 5 extends to and is anchored just below spinner means 10 on the upper end of cylinder 6. Wire 5 extends downward to and is anchored in the clean air inner take-off pipe 8 on the lower end. Thus charging wire 5 provides particle charging corona along the entire length of vertical cylinder 6. The inner wall of vertical cylinder 6 is grounded electrically and provides the means for establishing an electrial field between charging wire 5 and vertical cylinder 6 thus causing the charged contamination particles to move out of the contaminated air or gases and flow to the inner wall surface of vertical cylinder 6 where they are flushed out by a flushing means. Typically, r -7-..~

1137~;~7 a 0.008-inch dlameter charglng wlre 19 uset in a 4 or 8-inch dlameter stalnless steel tube. Howe~er, smsller or larger wlrQs can be u~ed dependlng on the ~echanlcal ~trength of the ~ire and applled voltage. The flushing means can be any compatlble flult wlth the proces~ but i8 usually waeer, Upper lnsulator 2 i9 fa~tened tlrectly to lnsulatlng cylindrical csp 3 whlle lower insulator 2 is supported by a metal rot 11 located and affixed horlzontally across the lower end of the unit. (If upper cap

3 i9 msde of metal, the upper lnsulator 2 can be unted on an insulatln~ bushlng in the cap and the electrical connec-elon made throu~h th~ bushlng.) Cyllnder 6 extends from upper water inlet 4 to low-r water outlet 7. Tube lengths of l to 5 feet have been te~ted, and generally, the longer tubes are preferred for higher flow rates. Wster to flush the uall of cylinder 6 ls supplled through an annulsr slot 12 at the upper ent of cylin-der 6 thus sllowlng for complete 360 wettlng of i~slde cyllndrlcal wall surfaces. The walls of cyllnter 6 are etchet for better and ~ore complete wettlng. After flowlng town the inslde wall of cylinder 6 ln a swirllng tlon, the water flushes out dust or contaminants from inner wall cyllnder 6, and the contamlnated water drops lnto an annular catch sump 13 whlch is formcd 360 around the bottom of cyllnder 6 ant between cyllnter 6 ant a smsller clean air inner take-off pipe 8 which e~tends upwart into the bottcm 1~37~7 end of cylinder 6. Thus the outlet end comprises a clean air inner take-off pipe 8 which extends into the outlet end of cylindrical cylinder 6.
- The upstream end of inner take-off pipe 8 may be angled at a (figure 4) with respect to the vertical axis.
The angle or flare in the upstream end of the inner-take-off pipe serves a very important function. In units such as the instant invention a turbulent separation phenomenon may occur where the flow of air abruptly crosses a sharp surface. Thus in straight inner take-off pipe design a pressure drop or turbulence will occur at the leading edge of the pipe. Thus the i~stant invention may be flared or angled at the leading or upstream edge of the inner take-off pipe thus eliminating this turbulent separation phenomenon. This angle is formed just above catch sump 13 and is angled outwardly with respect to the vertical axis wherein a is about 10 to 30 . However, the angle chosen must not interfere with the downward flow of water on the inner surfaces of cylinder 6. Therefore, sufficient room between the upper edge of inner take-off pipe 8 and the inside surface of vertical cylinder 6 must be insured. In this manner, efficient gathering of the clean air can be accomplished while the entrained particles are separately removed in the flush water. This is a significant feature of the invention in that it allows the clean air to be gathered without passing through the .

1~L374Z7 entrained flush water and thus the clean air can be recycled back lnto the work room where the contamination is being drawn from (see flgure 5). Without this recycle feature, the requlremeDts for addltional clean alr or some means of feeding alr lnto the room would become prohibitlvely expenslve and reduce the inventlon to extreme de~lgn limitatlons.
Thus air enterlng cylinder 6 at the upper end i9 caused to rotate by tangentlal spinner 10 as shown in figures 1 and 2, Hlgh voltage is appllet to wire 5 to produce corona and unipolar ions at the wlre whlch charge the dust or contaminant partlcles ln the alr or gas. As the gas/alr flows through cylinder 6 the charged dust/
contaminant ls driven to the walls or inner surface of cyllnder 6 by the radial electrical field set up within the cyllnder and by centrlfugal forces produced by the rotating gas flow. Water introduced through upper lnlet

4 flows down the inner surface of cyllnder 6 ant flushes the preclpitated dust/contaminant into water sump 13 where it flows out through water outlet 7. The rotational ~:
~ovement of the air also induces rotational flow of the water which assists in wetting the surface of cylinter 6 unifor~ily. Thus clean air is expelled at the lower ent of cylinder 6 through inner take-off clean air pipe 8, and is recycled back to the work area (flgure 5).
There are a number of crltlcal design feature~ which have produced unsual but great strides in the fleld of cotton ~374Z,7 dust removal. The instant invention is capable of handling exceptionally large volumes of air flow through very small equipment si~es. The critical parameters set out by design and arrived at through emperical testing are as follows:
The voltage to produce the corona ranges from about 30 kv to 60 kv.
The diameter of the vertically positioned cylinder ranges from 4 inches to 8 inches and can be scaled to smaller or larger units.
The length of the cylinder ranges from about 1 ft to 5.5 ft and can be scaled to smaller or larger units. The flow of water for flushing ranges from about 0.15 to 0.75 gal/min. The sxial velocity of air ranges from about 20 ft/sec to 50 ft/sec. These parameters are incorporated on a ratio of about 1:6 to 1:12 diameter of cylinder to length of cylinder; and a ratio of about 15 kv:l inch of radius. The flow of air, flush water, are adjusted accordingly. Thus a new and synergistic result is achieved when incorporating the above design parameters as outlined. 99~
efficiencies are achieved using the above parameters at 20 to 50 ft/sec velocities of sir flow wherein under current conditions of conventional precipitators or dust removal equipment this efficiency would fall to 50-70% when trying to handle the same high volume of flow since they are designed not to exceed a nominal range of 2 to 10 ft/sec flow velocities. It should be noted that the ratio of diameter to length of cylinder is a critical feature to achieve the best results.
For example with a 4-inch-OD cylinder, negative potentials of 30 kV produced operating currents of about 2.1 to 2.4 ma and about 6 to 8 ma with 2 and 4 foot cylinder lengths, 11379~Z7 respQctively. Fro~ about 0.18 to ~.35 gpm of water was needet eo flush AC fine test dust or fine cotton du6t from the walls effectively. Efficienclas greater than 99 percent, were achieved wlth gas flow rat~s of 200 cfm in the 4-foct cyllnder lengths and with pres6ure drops less than 4 inches of water. Comparable efflclency was demonstrated wlth positlve voltage also. Uith a larger 8-inch-OD cylinder, a negatlve potentlal of 60 kV producet an operating current of about 7 ma in a 5.5 foot cylinder length. With the larger cyli~der, efficiency greater than 99 percent was demonstrated at 800 cfm with an operating pressure of only 2 lnches of water, and a water flow rate of 0.35 gpm was needed to flush the walls.
The optimum perfor~ance of both the 4-incb ant 8-lnch dlameter wet wall electroinertial units is attained with axial gas velociti~ of about 2300 fpm. This provides a processing rate of about 2300 cfm/sq. ft. of cross-sectioDal area of the unit. Thus a 4-inch unit operates best at about a capacity of 200 cfm and th~ 8-inch unit operates with a capacity of about 800 cfm. Operating with la~ger disrleter units ls certainly possible theoretically, but this will pO8Q a practical problem as to the economics and safety of operating at voltages exceedin& 100 kV. Therefore, combination of more than one 6mall unit of the optimum size arranged as in figure 3 represents th~ re favorable condltion and hence emphaslze the unique importance of one part of the instant inventlon, th~t is, the crltical rstio of velocity of gas to cross-1~379~Z~

~ectional area of cyllnder diameter. Thls _ _ ratlo is set out by the results of the 4-inch-dlameter and 8-inch-dlameter cyllnders whlch have been demonstrated to produce the hlgh efflciency of duAt re val ln any conflguratlon cyllnder utilizing the cross-sectlonal area to ga~ veloc$ty ratio within the envelope of these parameters.
Referring now to figure 3 wherein another embodiment of the lnvention delineate~ a means of handllng large volumes of dirty air, such a~ cleaning systems in textile mills.
Flgure 3 shows a multiple cyllnder system of 11 cylinders.
U~ing 4-inch-diameter cyllnders, this unit would process up to 2200 cfm of dirty air. ~ater inlets 4 of each cylmder 6 i9 supplied from a common tank manifold 18. Water outlets 7 of each cylinder 6 drain3 into a common sump manlfold 19. Cylinders 6 are u~ted ln a vertlcal duct section 16 such that all of the alr flows through cylinders 6.
Passages between cyl~nders 6 are blocked by water manifold 18 and by a baffle plate 20 at the entrance end. Instead of using tangentlal alr dellvery to rotate the gas stream, a set of hellcal vanes 21 i8 mountet in the entrance of each cylinder . Vanes 21 can be mate of an insulating materlal and thereby serve as a support for the upper end of charging wire 5. If vane~ 21 are made of metal, suitable lnsulating bushings are used to isolate charglng wlre 5 from the grount.
In practlcal situations in mills, the system is teslgned such that the dirty water collected in the sump ~ Oe= hoY~) i8 ' .~
`t 1~l37~Z7 cleaned by flltering out the dlrt on a rotary screen. The clean water ls recycled to water tank manifold 18 for reuse.
Further, the afore~ald unlt 18 intended to process gases contalnlng principally flne dust. In a cotton textile mill lt could be used in con~unctlon wlth condensers and other flrst-and second-stage alr cleaners that are deslgnet to re ve coarse trash and flbers.
The following emperlcal examples are clted to demonstrate the high efflciencles achleved using the unlque deslgn fçatures of the instant inventlon thus resultlng the synergistlc effects clalmed supra.
EXAMPLE I
A unit with a 4-lnch dlameter cylinder was tested wlth ` varlous lengths and flow rates up to 40 ft/sec. Efficiency ¦
in the range of 97 to 99 percent was demonstreated with sub-15 micron artiflclal cotton dust and greater than 99 percent with card trash_uslng a 2-ft tube length as shown ln Table I.
TABLE I. TRIALS WITH 4-INCH-DLA~ETER CYLINDER AT
2-FT. TUBE LENGTH AND -30 kV

. . ~
Clrcu-Dust Feed latlon Pressure Effi-Current Test Fed, Time, Water R2te, Drop ciency, ma Dust 8rams mln. 8P~ ft/sec in H20 Percent 2.4 AC Flne 1 5 -- 20 1.25 >99.0 2.4 AC Fine 1 5 - 40 1.25 >99.0 2.2. Cotton 10 12 0.24 20 1.25 98.1 Dust 2.2 Card 10 150.26 40 3.75 99.7 Trash 2.1 CGttOn 10 160.18 40 3.75 96.1 Dust 1~37427 A unit with an 8-inch diameter cylinder was tested with various lengths and flow rates up to 40 ft/sec. Efficiency in the range of 96 to 99 percent was demonstrated with sub-15 micron artificial cotton dust and greater than 99 percent with card trash.
Table II shows data from tests in which the unit was connected to the exhaust system on a card machine. Efficiency of about 97 percent was demonstrated with the fine card dust which passed through a prefilter to remove the large trash.

TABLE II. TESTS OF 8-INCH DIAMETER CYLINDER 66" LONG
10Circulation Pressure Rate Drop, Potential, Current, Efficiency, ft/sec. in. H20 kV ma percent 2.1 -67.5 7.0 96.4 34 2.7 -67.5 7.0 -97.3 39 3.8 -67.5 7.0 97.5 43 4.5 -67.5 7.0 97.1 AC fine test dust made by AC Spark Plug Division of General Motors Corp. was used to test the instant invention. AC fine test dust is a natural Arizona dust, processed by the AC Division of the General Motors Corp. which has a mean mass particle size of approximately 12 microns.
Above results thus substantiate the combination of the electrical and inertial effects is additive and produces higher collection efficiency at high flow rates than is possible with electrostatic effects alone, and the pressure drop is lower than normally necessary to achieve high efficiency in a cyclone. The unit was designed for handling fine cotton dust (less than 15 microns), and tests have shown that the 8-inch diameter unit with a 66-inch cylinder will remove up to 99 percent of the cotton dust when the flow rate is as high as 800 cfm with only about 10.5 sq. ft.

. . ... . . . . . .

, 1137~7 of collector surface (13.1 sq. ft/l,000 cEm of gas flow). In the 8-inch diameter cylinder, the axial Elow velocity at 800 cfm is about 38.5 fps. Also, the twisting action ~f the air flow causes the water to flow in a spiral path down the wall of the cylinder. This provides for more effective scrubbing, and the wall of the cylinder ordinarily can be cleaned with as little as 0.35 gallons of water per minute (less than 0.5 gpm of water per 1,000 cfm of air flow). This is compared to single-state precipitators of conventional design which achieve efficiencies of about 99 percent with flow velocities in the range of 2 to 10 fps.
In most precipitators, the particulate material is collected as a dry cake on the plates or wall of the tube.
About 100 to 500 sq. ft. of collector surface is needed per 1,000 cfm of gas flow depending on the application. It can be readily concluded from this data that the vast difference between the surface area of the instant invention and that necessary for a conventional electrostatic precipitator rein-forces our conclusions of an important synergistic result achieved using the design parameters of the instant invention. In conventional precipitators, the collector is rapped periodically to release the cake which falls into bins. Depending on the electrical nature of the cake, the collected material can affect the charging current, causing arcing, reduce the effective field strength, and produce a condition which causes back corona. The net effect is that performance of the precipitator is affected adversely and the size of the unit must be increased and the operating voltage must be set at a low value to offset the adverse effect of the cake. Rapping to release the cake often results in ~l -16-1~374Zq some reentrainment of the collected material, and errosion of the cake must be avoided by keeping the gas flow rate relatively low. Further, cakes of combustible materials such as cotton dust constitute a fire hazard in dry precipitators ~here arcs are likely to occur in the course of normal operation.

'.

Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An inertial- electrostatic precipitator system for decontaminating a gas stream having particles dispersed therein, the particles including fines of under 10 microns; said system comprising:
A. a vertically-mounted collector tube having an upper inlet and a lower outlet;
B. means supplying an electrically-conductive liquid to the inlet in a full circle thereabout to create downflowing liquid on the inner wall of the tube;
C. an annular catch sump adjacent the outlet to receive the downflowing liquid from the tube;
D. means feeding said gas stream having particles dispersed therein into the inlet at high velocity and for imparting rotational motion thereto to create a centrifugal force inducing at least the particles of over 10 microns to migrate toward the downflowing liquid to be washed down into the sump, said velocity being sufficient to cause the rotational motion of the gas stream to induce spiral flow of the liquid in the downflowing liquid whereby the downflowing liquid uniformly wets the inner wall of the tube;
E. a discharge electrode coaxially disposed within the tube;
F. means to impress a high voltage between the discharge electrode and the downflowing liquid to create an electrostatic field therebetween and to charge the particles dispersed in the gas to further induce the particles including the fines to migrate toward the downflowing liquid, thereby substantially fully decontaminating the gas stream;

G. a take-off pipe inserted in the outlet and spaced from the inner wall of the tube carrying the downflowing liquid to form an exhaust for the decontaminated gas stream which is isolated from the downflowing liquid.

2. A system as set forth in Claim 1 wherein the upstream end of the take-off pipe is outwardly flared to minimize air turbulance at the leading edge of the pipe.

3. A system as set forth in Claim 1 wherein the means to impart rotational motion to the air stream comprises a tangential air spinner.

4. A system as set forth in Claim 1 wherein the means to impart rotational motion to the air stream comprises a vane-type air spinner.

5. A system as set forth in Claim 1 wherein said means to feed liquid into the inlet comprises an annular slot at the inlet of the tube to permit complete 360° wetting of the inner wall.

6. A system as set forth in Claim 1 wherein said discharge electrode comprises a single wire.

7. A system as set forth in Claim 1 further including a blower coupled to the take-off pipe to draw said air stream through said tube at said high velocity; said blower discharging said decontaminated stream into the atmosphere.