US2192249A

US2192249A - Apparatus and method for cleaning gases

Info

Publication number: US2192249A
Application number: US217748A
Authority: US
Inventors: Harry J White
Original assignee: Research Corp
Current assignee: Research Corp
Priority date: 1938-07-06
Filing date: 1938-07-06
Publication date: 1940-03-05
Anticipated expiration: 1957-03-05

Description

March 5, 1940. I wHlTE 2,192,249

APPARATUS AND METHOD FOR CLEANING GASES Filed July 6, 1938 3 Sheets-Shet 1 ll ll flaw Wind far-mfg March 5, 1940. w rr 2,192,249

APPARATUS AND METHOD FOR CLEANING GASES Filed July 6, 1958 3 Shets-Sheet 2 1/1/11, IlIIIIl/IIIIII March 5, 1940. ,J; w n' 2,192,249

APPARATUS AND METHOD FOR CLEANING GASES Filed July 6, 1938 3 Sheets-Sheet 3 Patented Mar. 5, 1940 UNITED STATES APPARATUS AND METHOD FOR CLEANING GASES Harry J. White, Los Angcles, (Zalii.l asslgnor to Research Corporation, New York, N. Y., a cornotation of New York Application July 6, 1938, Serial No. 211,748

25 Claims.

This invention relates broadly to the cleaning of gases, and more specifically to an apparatus for electrically precipitating suspended particles from gases comprising a two-stage precipitator 6 including a collecting electrode which may be kept covered with a liquid film. The invention is particularly directed to improvements in electrical precipitation apparatus of the type described in a copending application of Evald Anderson, Serial Number 211,306, filed June 1, 1938.

In the following description and in the appended claims, the term discharge electrode will be understood to designate an electrode that facilitates corona discharge therefrom, because it has a configuration that establishes su iiciently high potential gradient at or near its surface to create corona discharge before there is a disruptive discharge or spark-over. The term non-discharging electrode will be understood to designate an electrode that minimizes or prevents corona discharge therefrom because it has a configuration that establishes a sufiiciently low field concentration at or near the surface. to suppress corona discharge at elevated potentials below the voltage required for disruptive discharge or spark-over.

The expression precipitator of the two-stage wet electrode type is intended to include not only those precipitators in which a liquid film is provided by supplying liquid to the apparatus from a reservoir, but also is intended to include precipitators in which the liquid film is formed on'the collecting electrode by precipitation of liquid mistfrom a gas stream, or by both these actions in combination. Thus, a precipitator of the two-stage wet electrode type may be employed for the precipitation of solid particles alone, liquid particles alone, or both solid and liquid particles together. In thelatter case, if 40 the proportion of liquid to solids in the gas is not sufficient to provide the desired flushing of the solids, additional liquid may be supplied to the collecting surface for this purpose.

With the exception of the features of this invention relating to the establishment of liquid films on the collecting electrode, the various features of the invention are applicable to the precipitation of liquid mist.

Broadly, the apparatus of the Anderson application Serial Number 211,306, filed June 1, 1938, includes an electrical precipitation apparatus for the removal of suspended particles from gas streams which comprises a complementary electrode system including a discharge electrode element adapted .to create an ionizing field and an opposing non-discharging electrode, a second complementary electrode system comprising spaced non-discharging electrode elements, means for directing a gas to be treated successively between the complementary members of said electrode systems, means for impressing a high potential across the complementary electrodes of each of said electrode systems, and means for maintaining a liquid film on that one of the complementary electrodes of the second of said electrode systems, whose sign or polarity is opposite to that of the discharge electrode,'or upon said electrode element and also upon the non-discharging electrode of the first complementary electrode system.

Although the apparatus of said application permits em'cient operation at relatively high gas velocities, it has been found that efficiency of collection and capacity may be greatly increased in an apparatus of given size if suitable means are provided for the establishment and breaking of the liquid film upon the collecting electrode.

In an electrical precipitator in which a liquid film is maintained on an electrode surface on which the suspended solid particles are precipitated, it is necessary to provide means for sup-' plying the liquid to such electrode surface at one position, usually adjacent the upper end thereof, and also to remove the liquid from such electrode surface at another position, usually adjacent the lower end thereof. At the positionswherethe liquid is supplied to and removed-from the electrode surface, the smooth, continuous character of the liquidfilm is necessarily disturbed, and if such disturbances are permitted to occur at p0- j sitions within a region of strong electricfield between that electrode surface and the opposing electrode, excessive sparking tends to occur at the high potential difference which it is desired to maintain between the electrodes for effective precipitation. Furthermore, if such disturbances of the liquid film are permitted to occur at positions in contact with the moving gas stream, the gas stream tends to still further disrupt the liquid and to pick up droplets of the liquid, which is objectionable from several standpoints. If this disruption and picking up of liquid by the gas stream occurs at positions within the strong electric field between the electrodes, the tendency to objectionable sparking is seriously increased. Furthermore, if it occurs atpositions in the gas stream ahead of the electric fie1d, the resulting liquid droplets are carried forward into the electric field and tend to cause sparking and loss of efllciency, while, if it occurs at positions in --the gas stream beyond the electric field, the resulting liquid droplets are carried away by the gas stream instead of forming part of the desired liquid film.

The apparatus of the present invention includes means for establishing a continuous film of liquid upon a portion of the electrode to be wetted which is removed from the direct line of flow of the gas stream and also removed from the region of strong electric field, means for conducting the film of liquid so established into the collecting zone of the apparatus, means for flowing the liquid film over the electrode surface to be wetted, and means for removing the film from the surface of the wetted electrode in a quiescent zone remote from the direct line of flow of the gas stream and also removed from the region of strong electric field. Inconsequence of these improvements, at very uniform film of'llquid is caused to fiow over the surface of the electrode, which film is highly resistant to disturbing infiuences brought about by the current of gas adjacent thereto, whereby gas streams at high velocities may be directed successfully through the apparatus without disturbing the smoothness and continuity of the liquid film.

The maintenance of a smooth liquid film is desirable as a means for overcoming objectionable sparking, particularly between the non-discharg= ing collecting electrodes of the collecting stage. The cause of such sparking is that the moving .gas causes rippling of the liquid film with resultant concentration of the electric field. at the ripple protuberances, which enhances the elec tro-mechanlcal forces on the protuberances and tends to exaggerate the ripples. If this eiiect becomes pronounced, an actual break in the liquid film occurs and liquid drops are formed. These drops are charged at such polarity that they are attracted to the opposing high tension electrode. Each drop becomes elongated in the direction of the electric field and a spark will jump between the electrodes in consequence of the decrease in efiective smcing in the neighborhood of the elongated drop of liquid.

It has been found that the linear gas velocity in the individual pipes of the apparatus of this invention may be substantially increased if turbugas and minimize turbulence.

lent flow is avoided. Turbulent gas fiow, with its attendant swirling motion and eddy currents, exerts a disruptive effect tending to destroy the smoothness and continuity of the liquid film upon the inside surface of the tubular electrode, which results in the tearing awayof droplets of water from said surface and causes sparking between the complementary electrodes. The velocity of the gas stream at which this effect becomes pronounced is herein referred to as the critical velocity. In an apparatus of given size, the critical velocity may be increased by providing suitable vanes at the gas inlet ends of the pipes, which vanes straighten the line of flow of the construction, the vanes take the form of a gridlike structure mounted in the inlet nipples at the bottoms of the individual pipes.

In a two-stage precipitator of the wet-electrode type, it is desirable that the central electrode member and the surrounding tubular electrode member be accurately centered and aligned. Accurate positioning of the electrode members with respect to each other is essential in order to create uniform electric field conditions and to minimize the tendency of disturbing the smooth-- In the preferredness of the liquid film either by non-uniform electrical conditions or non-uniform gas flow.

In view of these considerations, the invention includes means for adjusting the position of the electrodes at all points of suspension. including mea'nsfor lateral adjustment of one or both of the electrode elements, and also for angular adjustment of one or both of these elements with respect to the vertical.

It is a general object of this invention to provide an improved electrical precipitator of the separated field type employing a'wet electrode.

A further object is to provide in a two-stage wet-electrode precipitator means for establishing and breaking the liquid film in regions removed from the fiowing stream of gas and also removed from the region of strong electric field..

stage wet-electrode precipitator.

The accomplishment of these objects, as well as others which will appear hereinafter, will be more particularly described and pointed out with reference to the accompanying drawings in which:

Hg. 1 is a sectional elevation of one form of apparatus for carrying out the objects of this invention;

Fig. 2 is an elevation in partial section of the apparatus of Fig. 1 taken at right angles thereto:

Fig. 3 is a plan view of the top of the interior of the apparatus of Figs. 1 and 2;

Fig. 4 is a detail in section of a portion of a central electrode assembly showing tapered washer means for angularly adjusting said electrode;

Fig. 5 is a sectional view of a modified unltpipe precipitator;

Fig. 8 is a sectional. view along the plane 6-8 of Fig. 5:

Fig. 7 is another modified unit pipe precipitator shown in section, and

Figs. 8 to 11 are sectional views showing liquid film-distributing devices for use in the apparatus of the invention.

Like reference numbers refer to corresponding parts in the several figures. The apparatus of Figs. 1, 2 and 3 is a two-stage wet-electrode precipitator comprising four precipitating units arranged in parallel, all the units being supplied with gas to be treated from a common inlet-header l and all units being adapted to exhaust the treated gas into a common outletheader 2. A common source likewise is provided for supplying liquid to the individual units, and a common sump means is provided to receive the diluent liquid. The means for applying a high potential across the elements of the complementary electrode assemblies may be a single high potential source. Parts common to all precipitation units will be described with reference to the unit generally designated at 3.

The apparatus is encased in a cylindrical housing 4, preferably constructed of sheet metal, such as galvanized iron, or other suitable material, and

2,192,949 partitioned into three sections l, 5 and 2'by suitable metal plates. The bottom section I comprises thb lower or inlet-header and is included between bottom plate 6 and inlet-header plate 1. Gas inlet means is provided at 8 in the form of a metal duct. of the housing is included between the lower header plate 1 and the upper header plate 9. The bottom portion. of this intermediate space forms a sump for receiving liquid discharged from the precipitation units and drain pipe l serves to remove the accumulation of discharged liquid from the apparatus. The top section 2,- included between upper header plate 9 and top plate H, provides means for receiving treated gas, and is designated the outlet header. Gas outlet means l2 leads the treated gas from the apparatus to the space where treated gas is wanted.

The precipitating units 3 are disposed between the upper and lower headers through suitable apertures in the respective header plates. The

joints are effectively sealed against leakage of gas from the headers into the intermediate space and leakage of wetting liquid from the intermediate space to the lower header by suitable gaskets or other means. The precipitating unit comprises essentially a tubular electrode member l3, for example, of cast iron or copper, either cast, drawn, or rolled and welded, which electrode member is adapted to accommodate a stream of gas flowing upward therethrough, and to provide a smooth inside surface over which a film of liquid is caused to flow in a downward direction under the influence of gravity. Disposed within and coaxially of the tubular. electrode member is a complementary central electrode assembly, sometimes referred to as a high tension electrode, the lower part of which comprises a fine wire discharge electrode 26 adapted to create an ionizing field in cooperation with the surrounding tubular electrode, and the upper part of which comprises an extended surface electrode of relatively large diameter adapted to provide a static electric precipitating field free from corona discharge in cooperation with that part of the tubular electrode I3 which surrounds it.

The lower end of the central high tension electrode assemblyis positioned somewhat above the lower end of the tubular electrode l3 where the liquid film is broken, as described hereinafter, so that the breaking of the liquid film at the point where said *film'is removed from the surface of said tubular electrode, occurs at a position entirely removed from the electric field.

The individual central electrode assemblies are supported solely from their upper ends which are secured to a spider hanger [5 which in turn is supported by an insulating support iii, of porcelain or other dielectric material, secured upon leveling plate I'l. This plate and the supported electrode assemblies may be leveled bodily with respect to the top header plate 9 by means of four small leveling screws 20, which pass through the leveling plate and bear on the header plate, as shown in Fig. 3. The leveling plate may be secured in adjusted position by means of bolts 2| through the leveling plate and header plate.

Conductor l8 leads from the spider I5 through insulator bushing ii! to the negative terminal of a source of high tension current, not shown. From the positive terminal of the current source, connectionis made with the housing 4, either directly or through ground as indicated. The central electrode assemblies are negatively charged through conductor l8 and spider I 5, while the The intermediate section 5 tubular electrode members are positively charged by connection with the source of current through the metallic housing.

The individual central electrode assemblies are constructed as shown in Fig. 1. Into a suitably threaded hemispherical metallic cap piece 22 is screwed one end of steel tie rod 23 which suspends the entire central assembly from the end of one of the arms of the spider hanger IS. A tubular sleeve 24, made of copper or other metal, and having its outside diameter the same as the diameter of the hemispherical cap piece, is slipped over the tie rod and seated on a shoulder suitably recessed in the upper part of the cap piece. A retaining disc 25 is screwed tightly 'down on the projecting end of the tie rod to engage the upper rim of the tubular'sleeve and to unite the parts of the central assembly into a unit.

understood by persons skilled in the art, electrode sections having exposed sections of relatively small radius of curvature, such as is provided in this case by the wire 26, bring about silent or corona discharge when a high potential is applied to the central electrode. In cooperation with that part of the tubular electrode surrounding it, the fine wire discharge element produces an ionizing field which eilectively charges the suspended particles in the gas stream flowing through the apparatus.

The central electrode assembly, provided with the discharge electrode described, is mounted on one of the arms of the spider hanger l5 as shown in' Fig.4. A pair of chamfered washers 29, each having one face cut at a small angle of the order of a few degrees to the other face thereof, are slipped over the projecting threaded end of the rod 23, and the assembly is then secured in the hanger l5 by means of washer and nut 3|.

The hole 32, through which tie rod 23 passes, is

Means also may be provided if desired, for

laterally adjusting the tubular electrodes l3 and for adjusting them with respect to the vertical, as illustrated in Fig. 5. Tubular electrode i3 is flared out at the top to accommodate'a liquid film-establishing means, and this expanded portion serves to suspend the tube in the apparatus by engagement with a collar assembly which perm ts lateral adjustment of the top of the electrode tube with respect to top header plate 9. The collar assembly comprises two

rings

33 and 35 including between them a rubber gasket 34. The gasket provides a gas-tight fit around the pipe, but at the same time permits the pipe to be tilted so as to permit lateral adjustment of the lower end of the pipe for the purpose of vertical alignment thereof. Lateral adjustment of the collar assembly, and with it the top of the pipe, may be effected within the clearance between the pipe and the top-header plate 9. The

bolt holes 38', are made somewhat larger than the bolts 36 to permit this adlustment.

The length of the tubular electrode I3 is such that the bottom of the tube, comes within a short distance, for example, one or two inches, of the bottom header plate I. A gas inlet nipple 31 is provided as means for introducing gas to be treated to the precipitation unit. This nipple is mounted on the lower header plate I by means of a flange 38 welded to the nipple andadjustably clamped between a gasket 39, which bears against the bottom header plate, and a ring 40 by means of bolts M. 'The nipple has a smaller diameter than the pipe I3 and extends into the bottom of the pipe. Spacing lugs 42, welded to th nipple, frictionaily engage the inside of the pipe to maintain it in fixed relationshipwith the nipple. Lateral adjustment of the lower end of the pipe is accomplished by lateral adjustment of the nipple 31 with respect to its adjacent header plate.

If desired, the means for adjusting the tubular electrodes I3 may be dispensed with when the means above described for adjustment of the central high tension electrode assemblies is such as to provide all necessary lateral adjustment and alignment of the complementary electrodes of each unit relative to one another. Thus, as illustrated in Fig; 1, each tubular electrode may be supported in substantially fixed lateral position upon the upper header plate 9, and each nipple 31 may be provided with a flange welded, bolted or otherwise secured to the bottom header plate 1. Similarly, when adjusting means are provided for the tubular electrodes, such as illustrated in Fig. 5, and are such as to permit all lateral adjustment and alignment necessary to provide uniform spacing between the complementary electrodes of each unit, the means for adjustment of the central high tension electrode assemblies may be omitted.

It has been found that in order to maintain.v

a uniform film of liquid flowing down the inside of the tubular electrode, it is desirable to establish and break the film in a region removed from the gas stream and from the electric field. If this is not done, mechanical and electrical influences disturb the liquid film at its place of establishment and prevent the proper distribution of the film over the surface of the electrode, or disturb the film where it is removed from the surface of the pipe causing formation of liquid drops which are entrained in the gas stream and carried into the ionization and precipitation zones to cause undesired sparking between complementary electrode members.

To overcome these difficulties, a method and means have been provided for establishing and for breaking the liquid film.

Broadly, the method comprises forming a continuous film of liquid at a position out of contact with the gas stream and remote from the region of the electric field, flowing the film in unbroken extended portion ofthe tube removed from the region of the gas stream, and means for shielding the outlet of said liquid supply member from the influence of the electric forces set up in the apparatus.

A preferred film-establishing means is shown at 43 in Figs. 1, 2 and 3, but is shown with great particularity at 43 in Fig. 5, and will be described with reference to this latter figure. The liquid supply means is an annular ring 43 which may be made by brazing together the ends of a brass tube to form a continuous ring. The outside of the ring is pierced with spray holes 44 distributed around the periphery thereof. The tube at suitable intervals is provided with spacing rings 45, of suitable gauge copper wire, to prevent direct contact of the ring 43 with the flared portion of pipe I3. The space between the annular ring and the inside surface of pipe I3 provides in effect an annular orifice through which the wetting liquid flows. Liquid is supplied to the annular ring through pipe 46, emerges through holes .4, and forms a pool of liquid between the annular ring and the inside surface of pipe I3, the spacing between these members being such that capillary forces are sufllcient to maintain a continuous annular pool of liquid therebetween as long as liquid is supplied to the upper end of the orifice. It is desirable that the spray holes 44 be placed slightly above the line of closest approach between the annular ring 43 and the flared portion of pipe I3, so that the liquid emerges into the trough-shaped space above this line of closest approach and is shielded from both the electric field and the gas flow. In operation, liquid is continuously supplied to the pool, which in turn continuously feeds a smooth film of liquid through the annular orifice upon the flared-out portion of the surface of pipe I3, whence the liquid flows down the inside surface of the pipe in a smooth and unbroken film- .The liquid film is established in the flared-out portion of pipe I3 remote from the region of the gas stream, and the annular ring 43 effectively shields the place of formation of the liquid film from disturbing electric influences. Thus the film is laid down under substantially ideal conditions.

The liquid supply system is shown clearly in Figs. 1, 2 and 3. The main liquid supply pipe 41 conducts the wetting liquid, for example water, to the precipitator from a suitable source of supply. Preferably pipe 41 enters the apparatus through the side wall of the lower header I, and thence is led through the bottom header plate I nearly to the top of the intermediate space 5, at which point it is divided into two smaller horizontal pipes 48, which are led up through the top header plate 9 through suitable glands, which serve to maintain the risers 50 in fixed relationship with top header plate 9. Where the liquid conveying pipes pass through partitions between gas-tight chambers, leakage of gas is prevented by the use of suitable packing glands. The risers are fitted with crosses at points slightly above the tops of the tubular electrodes I3. From these crosses, pipes 46 connect with annular liquid distributing members 43 through valves 49, which control the flow of liquid to the individual precipitating units.

Means for breaking the liquid film at the bottom of the tubular electrode out of contact with the gas stream andshielded from electrical forces in the apparatus, comprise an inlet nipple extending into the tubular electrode effectively to shield the lower lip of the tubular electrode member from electrical forces and to introduce the gas stream into the precipitation tube at a point beyond said lower lip in the direction of gas flow.

This nipple provides a quiescent zone substantially free from gas movement about the lower end of the tubular member which permits the downwardly flowing liquid film to fall away from the tubular member without'danger of liquid drops being entrained in the gas stream.

One form of inlet nipple is shown at 3'! in Fig. 5, and its construction and auxiliary function of positioning the lower end of tubular electrode l3 already have been described. It will be seen that the upper end of nipple 31 is positioned a sufiicient distance below the lower end of the central high tension electrode assembly (1. e., below the lower end of the discharge electrode 26) so as to be substantially outside the region of high electric field between the complementary electrode members, the spacing of the upper edge of said nipple from the lower end of the discharge electrode being considerably greater than the spacing between said discharge electrode and the opposing portion of the tubular electrode member l3. Therefore the liquid is caused to fiow in a continuous, smooth film throughout-the entire length of the electric field to a position removed from the electric field and out of contact with the gas stream, where the film broken in a quiescent zone and the liquid conducted away, without danger of causing sparking or entrainment of liquid particles.

Another form of inlet nipple for accomplishing the same purposes is shown in Fig. '7, in which the nipple generally is designated by the reference number 52. The nipple itself preferably is cast in aluminum or other suitable metal, in the form of a short pipe with one end rolled back upon itself to form between the outside wall 53 and inside wall 54 an annular U-shaped receiving trough 58. The receiving trough is of dimensions suitable to accommodate the lower end of'tubular electrode member 55, and is attached to said tubular member by means of evenly spaced lugs 56 welded to the tubular member and screwed to the outside wall 53 of the inlet nipple with cap screws 51.

Liquid which fiows down the inner surface of tube 55 is caught in the U-shaped trough 58 and led away to any suitable reservoir, not shown, through outlet 59.

The apparatus shown in Fig. 7 is a unit precipitator which may be used alone or which may be used in combination with a plurality of like units suitably arranged in a common housing.

To increase capacity, and thereby to lower the concentration of ozone and nitric oxide in the treated gas, it has been found that vanes provided at the point of inlet of gas to the treating units substantially increase the critical velocity of the gas. These vanes are advantageously positioned in the inlet nipple 31, as shown at 21 in Figs. 5 and 6. In this modification, the vanes, which are of light gauge sheet metal welded in place, divide the nipple into nine separate gas channels of almost equal cross-sectional area, but the invention is not limited to the structure shown; a greater or smaller number of vanes may be used to divide the nipple into a correspond-' ingly greater or smaller number of channels, or the vanes may be arranged so as to form a hexagonal honeycomb structure or any other suitable configuration. In the direction of gas flow, vertically as shown, the vanes extend practically the entire length of the inlet nipple. It is the function of these vanes to promote straight line gas flow through the treating chamber and to minimize the tendency of the gas to swirl and cause objectionable eddy currents which tend to disturb the smoothness of the liquid film on the inside of tubular electrode l3.

Although vanes are specifically shown only in Figs. 5 and 6, they may be used in all modifications of the apparatus of this invention. Other means for establishing liquid film at the t p of the tubular electrodes are shown in Figs. al 9, and 11. Each of these film-establishing means provides for laying down the liquid film on a portion of the tubular electrode shielded from the moving gas stream and the electric field. In Fig. 8, the liquid distributing element is a spray ring 60, similar in construction to the spray ring described in connection with Fig. 5, but spaced so far from the inner surface of tube 6| that no pool of liquid is maintained by capillary forces between the spray ring and the tube, and the lines of closest approach between the spray ring and the tube do not include in effect' an annular orifice. The distance between spray ring and tube may be of the order of onehalf inch. The sprays from spaced holes 62 are directed outwardly against the inside of tube 6! where the individual streamsimpinge upon the surface and coalesce to form a continuous film, which fiows down the tube under the influence of gravity. To eliminate spattering of the liquid, and as a shield to protect the region of film formation from the disturbing influences already referred to, an annular metal shield 63 is mounted upon the tube 6| by ears 64. The shield extends inside the spray ring and the lower edge 65 of the shield extends to within a distance from the inside oftube 6| of the same order as the distance of closest approach between the spray ring 60 and the side of the tube, so that the liquid film flows beneath it without touching.

The film-establishing means shown in Fig. 9 is of the overflow type. Wetting liquid is admitted to reservoir 56 through pipe 61, and rises in the reservoir until it flows over the lip of, and down the inside of, tube 68. Annular metal shield 69, suitably mounted to the rim of the reservoir extends over the lip of tube 68 and shields it from the gas stream and the electric field. The shield 69 also serves to prevent precipitation of solid particles on the lip of tube 68. If precipitation of solid particles on this lip were permitted to occur, it would eventually interrupt the fiow of liquid over the lip at certain points and result in the formation of dry spots or areas on the collecting surface. In a similar manner, the shield'members shown in connection with the other forms of film-establishing means herein described also serve this added function of preventing precipitation of solid particles at the position where the liquid is supplied to the surface of the tubular electrode. The distance between the points of closest approach of the shield and tube 68 is great enough so that the liquid film does not touch the shield, yet small enough so ,that gas movement at the lip of the tube is reduced to a minimum. y

In Fig. 10, an annular G-shaped metal filmestabli'shing means 10 is used. The film-establishing means is suitably attached to the tube 12, by ears II. The lower surface 13 of the ring substantially conforms in shape to the flared portion 14 of the tube. A small space is provided between the ring and the flared portion of the tube to form an annular orifice for the issuance of a liquid film. The orifice is of such dimensions that a film of liquid may be maintained by capillary action between the sides of the orifice. Wetting liquid is supplied to the ring through pipe 15, and this liquid fills the troughlike lower section of the ring and overflows through the orifice between ring and tube, forming a continuous smooth film. The ring, in addition to its function as a film-establishing means, performs the added function of a shielding means.

The film-establishing means shown in Fig. 11 is integral with the tubular electrode 16. To form the ring Ti, the top of the tube is flared out and then rolled in upon itself, the top edge 18 of the tube approaching, but not quite touching the flared out portion of the tube. vThis providesthe annular space 19, which forms an annular orifice for the establishment of the liquid film. The orifice is small enough so that capillary forces are sufficient to maintain a small pool of wetting liquid in the ring 11. Liquid is admitted to the ring through pipe 80 and fiows out through the orifice l9 and thence down the pipe in a smooth unbroken film. The overhang of ring 11 shields the orifice from disturbing mechanical and electrical influences.

The film-establishing means shown in Figs. 5, 10 and 11 all have in common an annular orifice of suificiently small radial width that a downwardly flowing film of liquid is formed by capillary action between the sides of the orifice. Capillary action keeps a continuous pool of liquid above the orifice, the pool being unbroken around the entire circumference of the orifice, and consequently the issuing film is free of breaks that permit dry spots to form on the electrode surface. Film-establishing means of this character has the particular advantage that the annular orifice need not be precisely level, as is the case with film-establishing means of the overflow type shown in Fig. 9 when the continuity of the the film depends on the uniform overflow over a level edge or weir. The advantages of this improved construction are particularly important in small precipitators in which it is a diificult job to keep the overflow edge exactly level at all times. The capillary ring may be added to the formof Fig. 9 by making the spacing between tube 68 and the inner lip of shield 69 sufiiciently small to form an orifice having the desired capillary action. With the means of Fig. 8', the sprays establish a continuous film,

but the capillary ring can be added by placing I either spray ring 60 or shield sufiiciently close to tube 6| to obtain the action described.

The several modifications of shielding members described provide ineffect a continuation of the straight portion of the tubular electrode member, whereby to direct the gas stream in substantially'straight' line flow from the precipitation zone past the liquid film-forming zone into the receiving header. In this manner, the liquid film is established in a zone away from the flow of gas and has an opportunity to become organized and smoothed before it comes in contact with the gas stream. Likewise. the shielding members, being grounded to the tubular elec- I ticles first are electrically charged in the ionizing 1. In the method of removing suspended particles from gases comprising subjecting a stream of gas to the action of a corona discharge, in a high tension electric field wherein the suspended particles are charged, subsequently passing the gas through a second high tension electric field substantially free of corona discharge and maintaining in said second field a substantially continuous film of liquid in a position to intercept the charged particles moving under the influence of said second field, the improvement which comprises forming a continuous film of liquid at a position out of contact with the stream of gas and remote from the region of the electric field,

and flowing said film in unbroken condition into said second electric field.

2. In the method of removing suspended particles from gases comprising subjectinga stream of gas to the action of a corona discharge in a high tension electric field wherein the suspended particles are charged, subsequently passing the gas through a second high tension electric field substantially free of corona discharge and maintaining in said second field a substantially continuousfilm of liquid in a position. to intercept the charged particles moving under the influence of said second field, the improvement which comprises forming a continuous film of liquid at a position out of contact with the stream of gas and remote from the region of the electric field, flowing saidfilm in unbroken condition out of .said field, and breaking the film at a position out of contact with the gas stream and remote from the region of the electric field.

3. In the method of removing suspended particles from gases comprising subjecting a stream of gas to the action of a corona discharge in a high tension electric field wherein the suspended particles are charged, subsequently passing the gas through a second high tension electric field substantially free of corona discharge and maintaining in said second field a substantially continuous film of liquid in a position to intercept the charged particles moving under the influence of said second field, the improvement which comprises flowing said film in unbroken condition out of said field, and breaking the film at a position out of contact with the gas stream and remote from the region of the electric field.

4. In an electrical precipitator of the two-stage wet-electrode type including a tubular electrode providing a collecting surface, a liquid film providing means comprising an annular liquid supply member adjacent the inner surface of an extended portion of the tubular electrode removed from the region of the gas stream, means forming in cooperation with the extended portion of the tube an annular liquid orifice adjacent the inner surface of the tube, and means for shielding the annular liquid .orifice from the influence of electric forces set up in the apparatus.

5. In an electrical precipitator of the two-stage 15 wet-electrode type including a tubular electrode providing a collecting surface, a liquid film providing means comprising an annular spray ring which directs a plurality of coalescing. sprays of water against an extended portion of the tubular electrode removedfrom the region of the gas stream and an annular shield member adjacent the spray ring which forms in effect an extension of the straight portion of the tubular electrode whereby to insulate the outlets of the spray ring and the area of impingement of the sprays against the extended portion of the tubularclectrode from liquid-disturbing electrical and mechanical influences.

6. In an electrical precipitator of the two-stage wet-electrode type including a tubular electrode providing a collecting surface, a liquid film pro-- viding means comprising an annular reservoir surrounding the top of the tubular electrode adapted to create a pool of liquid overflowing the lip of the tubular electrode into an extended'portion thereof removed from the region of the gas stream and an annular shield member adjacent the lip of the tubular electrode, said shield forming in effect an extension of the straight portion of said tubular electrode, whereby to insulate the lip of the tubular electrode from liquid-disturbing electrical and mechanical influences.

'7. In an electrical precipitator of the two-stage wet-electrode type including a tubular electrode providing a collecting surface, a liquid film providing means comprising an annular trough-like liquid supply member adjacent the inner surface of an extended portion of the tubular electrode removed from the region of the gas stream, the surface of the liquid-containing portion of the trough-like member adjacent the inner surface of the extended portion of the tubular electrode forming in cooperation therewith an annular liquid orifice, the said surface of the trough-like member being extended in the direction of gas flow in the apparatus to form in effect an extension of the straight portion of the tubular electrode whereby effectively to insulate the trough of the liquid supply member and the annular liquid orifice from liquid-disturbing electrical and mechanical influences.

8. In an electrical precipitator of the two-stage wet-electrode type including a tubular electrode providing a collecting surface, a liquid film providing means comprising an annular liquid supply member integral with the tubular electrode and formed as by flaring out the upper end of the tube and then rolling inwardly the lip thereof to form an annular ring, said lip cooperating with a section of the inside of the tube removed from the region of the gas stream to form an annular liquid orifice, a portion of the ring acting as a shield to insulate the annular liquid orifice from liquid-disturbing electrical and mechanical influences.

9. In an electrical precipitator of the two-stage wet-electrode type comprising opposing electrode means defining a charging section and a precipitating section in both of which a high potential electric field is maintained, one of said electrode means having a vertically extended collecting surface, and means for passing a stream of gas to be cleaned successively through said charging and precipitating section, the combination which comprises: means adjacent the upper end of said one electrode means for supplying liquid to the surface thereof and for shielding the position of supply to keep said position out of contact with the stream of gas and removed from the region of the electric field, to maintain a downwardly flowing film of liquid on said collecting surface, and means adjacent the lower end of said one electrode means to break said liquid film at a position out of contact with the gas stream and removed from the region of the electric field.

10. In a two-stage electrical precipitator, a high tension electrode comprising an upper rigid non-discharging section and a short discharge electrode element below said non-discharging section and supported thereby, supporting means engaging the upper end of said high tension electrode and wholly supporting the same, a tubular.

electrode surrounding and spaced from said high tension electrode and having its inner surface extending from a position adjacent the upper end of said high tension electrode to a position below the lower end of said high tension electrode, means for supplying liquid to the inner surface of said tubular electrode adjacent the upper end thereof, a gas inlet nipple extending upwardly within the lower .end of said tubular electrode and having its upper edge spaced from said discharge electrode element by a distance greater than the spacing between said discharge electrode element and the inner surface of said tubular electrode, said nipple being of less diameter than said tubular electrode and being spaced therefrom to provide for downward flow of liquid on the inner surface of said tubular electrode and around said nipple.

11. In a two-stage electrical apparatus for the precipitation of liquid mist from a gas stream bearing particles of liquid mist, a high tension surrounding and spaced from said high tension electrode and having its inner surface extending from a position adjacent the upper end of said high tension electrode to a position below the lower end of said high tension electrode, a gas inlet nipple extending upwardly within the lower end of said tubular electrode and having its upper edge spaced from said discharge electrode element by a distance greater than the spacing between said discharge electrode element and the inner surface of said tubular electrode, said nipple being of less diameter than said tubularelectrode and being spaced therefrom to provide for downward fiow of liquid on the inner surface of said tubular electrode and around said nipple.

\ 12. In a two-stage electrical precipitator, a high tension electrode comprising an upper rigid non-discharging section and a short discharge electrode element below said non-discharging section and supported thereby, supporting means engaging the upper end of said high tension electrode and wholly supporting the same, a tubular electrode surrounding and spaced from said high tension electrode and having its inner surface extending from a position adjacent the upper end of said high tension electrode to a position below the lower end of said high tension electrode,

trode element and the inner surface of said tu- 75,

bular electrode, said nipple being of less diameter than said tubular electrode and being spaced therefrom to provide for downward flow of liquid on the inner surface of said tubular electrode and around said nipple, and means within said nipple to divide it into a plurality of separate gas channels. v

13. In a two-stage electrical precipitator, a high tension electrode comprising an upper rigid non-discharging section and a short discharge electrode element below said non-discharging section and supported thereby, supporting means engagingthe upper end of said high tension electrode and wholly supporting the same, a tubular electrode surrounding and spaced from said high tension electrode and having its inner surface extending from a position adjacent the upper end of said high tension electrode to a position below the lower end of said high tension electrode, means for supplying liquid to the inner surrface of said tubular electrode adjacent the upper end thereof, a gas inlet nipple extending upwardly within the lower end of said tubular electrode and having its upper edge spaced from said discharge electrode element by a distance greater than the spacing between said discharge electrode element and the inner surface of said tubular electrode, said nipple being of less diameter than said tubular electrode and being spaced therefrom to provide for downward flow of liquid on the inner surface of said tubular electrode and around said nipple, and vanes within said nipple and substantially parallel to the axis thereof to divide it into a plurality of separate gas channels.

14. In an electrical precipitator having a tubular collecting electrode and a rigid depending electrode assembly located centrally of the collecting electrode, the combination of: a hanger member; means attaching the central electrode assembly to the hanger member to support the electrode assembly at its upper end only; and an adjusting member interposed between the hanger member and the electrode assembly and adapted upon change in position to change the angular position of the electrode assembly with respect to the hanger member.

15. In an electrical precipitator having a tubular collecting electrode and a rigid depending electrode assembly located centrally of the collecting electrode, the combination of: a hanger member; means attaching the central electrode assembly to the hanger member to support the electrode assembly at its upper end only; and an adjusting member, having a pair of plane nonparallel faces, interposed between the hanger member and the electrode assembly and adapted upon change in position to change the angular 4 position of the electrode assembly with respect to the hanger member.

- 16. In an electrical precipitator having a tubular collecting electrode and a rigid depending electrode assembly located centrally of the collecting electrode, the combination of a hanger member; means attaching the central electrode assembly to the hanger member to support the electrode assembly at its upper end only; and a pair of washers, each having a pair of plane faces disposed at a small angle with respect to each other, interposed between the hanger member and the electrode assembly, the washers being adapted upon relative rotation to change the angular position of the electrode assembly with respect to the hanger member.

, 17. In an electrical precipitator having a tubular collecting electrode and a rigid depending electrode assembly located centrally of the collecting electrode, the combination of: a hanger member; means attaching the central electrode assembly to the hanger member to support the electrode assembly at its upper end only; and

' means in the hanegr receiving the attaching electrode assembly located centrally of the col- 'lecting electrode, the combination of ahanger member; means attaching the central electrode assembly to the hanger member to support the electrode assembly at its upper end only; means interposed between the hanger member and the electrode assembly and adapted upon change in position to change the angular position of the electrode assembly with respect to the hanger member; and means in the hanger receiving the attaching means and permitting lateral adjusting movementof the attaching means to laterally change the position of the electrode assembly wth respect to the hanger member.

19. In an electricalprecipitator, the combination comprising: a plurality of tubular collecting electrodes; a plurality of rigid electrode assemblies located one centrally of each collecting electrode; a common supporting structure for all the central electrodes; and means attaching each central electrode assembly individually to the common supporting structure to support the central electrode only at its upper end; said supporting structure including adjustment means for leveling the support and attached electrode assemblies as a unit.

20. In an electrical precipitator, the combination comprising: a plurality of tubular collecting electrodes; a plurality of rigid electrode assemblies located one centrally of each collecting electrode; a, common supporting structure for all the central electrodes; and means attaching each central electrode assembly individually to the common supporting structure to support the central electrode only at its upper end; said supporting structure including a base plate, a plurality of leveling screws adapted to adjust the base plate.

with reference to a fixed surface for leveling the support and attached electrode assemblies as a unit, and lock means securing the base plate in the electrode; and positioning means at the lower end of the electrodelaterally movable to position the lower end of the electrode.

22. In an electrical precipitator, the combina- I tion comprising: a tubular collecting electrode; an opposing electrode assembly located centrally of the tubular electrode; means suspending the tubular electrode near its upper end, engaging the electrode periphery to support the electrode and permit limited tilting motion of the electrode; and positioning means at the lower end of the electrode laterally movable to position the lower end of the electrode, said positioning means comprising an externally ribbed nipple extending upwardly within and slidably engaging the electrode, a, flange on the nipple and a pair of gripping members gripping between them the flange to hold the nipple in laterally adjusted positions.

23. In an electrical precipitator of the wetelectrode type, the combination of a tubular electrode providing a collecting surface and having an outwardly flared portion at its upper end; and liquid film providing means disposed within the flared portion of the electrode, said film providing means comprising an annular liquid supply means adjacent the inner surface of said flared portion and means for shielding the outlet of said supply means from the influence of electrical forces set up in the electrode.

24. In an electrical precipitator of the wet-electrode type, the combination of a tubular electrode providing a collecting surface and having an outwardly flared portion at its upper end; and liquid fllm providing means disposed within the flared portion of the electrode, said film providing means comprising an annular liquid distributing means adjacent the inner surface of said flared portion and means for shielding the film forming zone from disturbing electrical and mechanical influences. I

25. In an electrical precipitator of the wetelectrode type, the combination of a tubular electrode providing a collecting surface and having an outwardly flared portion at its upper end; an

annular member spaced from the inner surface of the electrode to form an annular orifice through which liquid flows downwardly over the inner surface of the electrode, the radial width of the orifice being small enough that capillary forces maintain a continuous pool of liquid above the orifice; and supply means for supplying liquid to the upper end of said orifice.