US3716966A - Wet elecrostatic precipitator - Google Patents

Abstract

(E( A DISCHARGE ELECTRODE STRUCTURE SUPPORTED WITHIN SAID PASSAGE, (F) MEANS TO APPLY A HIGH VOLTAGE BETWEEN SAID DISCHARGE ELECTRODE STRUCTURE AND BOTH OF SAID TUBES TO CAUSE MIGRATION OF PARTICLES IN SAID GAS TOWARD THE FILMS ON SAID TUBES AND THEREBY PRODUCE A CLEAN GAS, AND (G) OUTLET MEANS AT THE UPPER END OF SAID ANNULAR PASSAGE TO DISCHARGE THE CLEAN GAS INTO THE ATMOSPHERE, SAID OUTLET MEANS INCLUDING AN INVERTED FRUSTO-CONCIAL DEFLECTOR IN AXIAL ALIGNMENT WITH SAID TUBES TO DIRECT THE CLEAN GAS FROM SAID PASSAGE OUTWARDLY IN THE HORIZONTAL PLANE.
1. AN ELECTROSTATIC PRECIPITATOR FOR CLEANING CONTAMINATED GAS COMPRISING: (A) CONCENTRICALLY-ARRANGED INNER AND OUTER COLLECTOR TUBES DEFINING A VERTICALLY-DISPOSED ANNULAR GAS PASSAGE, (B) MEANS COUPLED TO A WELL TO DRAW LIQUID THEREFROM AND TO FEED THE LIQUID TO THE UPPER ENDS OF SAID TUBES TO PRODUCE A DOWNWARDLY-FLOWING AND SUBSTANTIALLY UNIFORM LIQUID FILM ON THOSE SURFACES OF SAID INNER AND OUTER TUBES WHICH LINE SAID PASSAGE, (C) CONCENTRICALLY-ARRANGED TROUGHS AT THE LOWER ENDS OF SAID TUBES TO RECEIVE THE DOWNWARDLY-FLOWING LIQUID THEREFROM AND TO DISCHARGE THE LIQUID INTO SAID WELL, (D) INLET MEANS TO INTRODUCE SAID CONTAMINATED GAS INTO THE LOWER END SAID ANNULAR PASSAGE BETWEEN SAID TROUGHS, SAID INLET MEANS INCLUDING MEANS TO ADMIT SAID GAS IN A HORIZONTAL PLANE AND FURTHER INCLUDING A FRUSTO-CONICAL DEFLECTOR IN AXIAL ALIGNMENT WITH SAID TUBES TO DIRECT CONTAMINATED GAS ENTERING IN THE HORIZONTAL PLANE UPWARDLY THROUGH THE VERTICALLY-DISPOSED ANNULAR PASSAGE,

Description

Feb. 20, 1973 A. P. DE SEVERSKY 3,716,966

WET ELECTROSTAT I C PREC IP I TATOR Filed Aug. 31, 1960 5 Sheets-Sheet 1 INVENTOR. Q y Aumq Horseman Arrows Feb. 20, 1973 A. P. DE SEVERSKY 3,716,

WET ELECTROSTATIC PRECIPITATOR Filed' Aug. 31, 1960 5 Sheets-Sheet 2 IN WIN TOR.

BY Awumq P 0: Jumps" nr' wers Feb. 20, 1973 A. P. DE S'EVERSKY 9 6 WET ELECTROSTATI C PR EC I PITATOR Filed Aug. 31, 1960 r 5 Sheets-Sheet I5v IN V EN TOR. Acumq 0! Sue Arm Feb. 20, 1973 A. P. DE SEVERSKY 3,715,966

WET ELECTROSTATIC PRECIPITATOR Filed Aug. 31, 1960 5 Sheets-Sheet 4 Hus: Gene-49AM Ti 1U. Mum

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6o canoe P 0: Screw a /W'W U.S. Cl. 55-118 4 Claims This invention relates generally to apparatus for clean ing contaminated gases and more particularly to a wet electrostatic precipitator of exceptional efficiency.

This application is a continuation-in-part of my copending application Ser. No. 855,369, filed Nov. 25, 1959, and issued Sept. 11, 1962 as Pat. 3,053,029, which copending application is a division of my original application Ser. No. 479,909, filed Jan. 5, 1955, and issued as Pat. 2,937,709 011 May 24, 1960.

vThe increase in atmospheric pollution and smog in modern communities has created a health hazard of major proportions and has become a matter of grave social concern. Air pollution is irnputable to many factors among which are the use of incinerators to burn household waste and various industrial operations which discharge combustion products into the atmosphere.

Electrostatic precipitators, both of the dry and wet type, have been used for cleaning contaminated gases, but such use has been limited mainly to industrial applications. There has not heretofore been available an inexpensive, efiicient and reliable precipitator for non-industrial users, to be installed for example in apartment houses so as to prevent the discharge into the atmosphere of particles emanating from incinerator and heating systems.

The present invention deals with a precipitator of the wet type wherein the contaminated gases are conveyed through an electrostatic field between electrode surfaces. Particles in the gas are precipitated onto a collecting surface constituted by a film of water flowing over a collector. Since the water carries the particles away continuously, a precipitator of this type is self-cleaning and is therefore particularly suited to non-industrial uses. This wet type of precipitator is also advantageously used for extracting radio-active particles from the atmosphere in case of fallout. The dry type of precipitator would accumulate the extracted particles and become so highly radioactive that it would become a hazard itself. By using the wet type of precipitator, the radioactive material is carried away by the liquid which may then be stored or treated to decontaminate. While the present invention will be described in connection with a wet precipitator, it will become apparent that certain features of the invention are also applicable to dry precipitators.

.One of the characteristic defects in existing wet precipitators arises from the fact that the liquid film is generally uneven and does not fully coat the collector surface. If the water is merely poured into the vertical collector tube of the precipitator, it tends to trickle down in separate streams and it is difficult to ensure that it will spread over the interior surface without an excessive flow of incoming water. As a result, dry patches appear on the collector and certain particles, such as carbon black, on reaching a dry area tend to give up their charge.'These particles acquire an opposite charge by induction and may experience sufficient force in a strong field to be moved back toward the other electrode into the gas stream. As a consequence, the particles pass out of the cleaner and are discharged into the atmosphere.

Accordingly, it is one object of the invention to provide an electrostatic precipitator of the water film type wherein water is caused to flow uniformly and smoothly on the walls of the collector tubes, and wherein dry patches are obviated. A significant feature of the inven- United States Patent tion resides in the fact that a Water distributor is provided which discharges multiple streams tangentially against the surface of the collector, the streams being divergent and intersecting.

Another factor which militates against the use of wet precipitators in non-industrial applications is the relatively high power requirements for the precipitator. It is the usual practice to pass the contaminated gas initially through a charging field in which a corona discharge is produced in order to ionize the suspended particles. The gas then passes through an electrostatic precipitating field which is free of corona discharge, this field acting to cause migration of the particles toward the collecting electrode. The use of a pre-ionization field involves a relatively high voltage and in conventional precipitators brings about a substantial current flow. The power requirements of the pre-ionization field when added to that of the precipitating field are considerable and make the operation of the standard precipitator costly.

It is therefore another object of the invention to provide a wet electrostatic precipitator of high efficiency which re quires substantially less power to operate than conventional gas cleaners.

A further object of the invention is to provide a power supply for a precipitator which generates pulsed voltages of high amplitude to produce an ionizing field.

Also an object of the invention is to provide a wet electrostatic precipitator which is of compact design and yet has a large gas cleaning capacity.

The wet precipitator in accordance with the invention is constituted by two concentric collector tubes, a water film being formed uniformly both on the outer surface of the inner tube and the inner surface of the outer tube by means of distributors producing multiple diverging streams of water which are introduced tangentially to the collector surface and intersect thereon. Precipitator and corona discharge electrodes are suspended in the annular passage between the two tubes to remove particles from. the gas conveyed vertically thereon. Corona discharge voltages are applied in pulsatory form, whereas the lower precipitation voltage is maintained at a constant level.

For a better understanding of the invention as well as other features and objects thereof, reference is made to the following detailed description to be read in conjunction with the accompanying drawing wherein like components in the several views are identified by like reference numerals.

In the drawings:

FIG. 1 is a perspective view of the precipitator cabinet.

FIG. 2 is a section taken through the precipitator structure in the vertical plane.

FIG. 3 is a transverse section taken in the plane indicated by line 3-3 in FIG. 2.

FIG. 4 is a linear projection of the flange water distributor.

FIG. 5 is a plan view of the flange.

FIG. 6 is an end view of the flange.

FIG. 7 shows the water distribution pattern produced by the flange.

FIG. 8 schematically shows one preferred form of preionization and collector electrode structure in accordance with the invention.

FIG. 9 schematically shows another form of pre-ionization and collector electrode structure in accordance with the invention.

FIG. 10 shows the waveform of voltage applied to the structure shown in FIG. 9.

FIG. 1 1 is a schematic view of a pulsating high voltage supply suitable for use in conjunction with the present invention.

FIG. 12 is a sectional view of a preferred form of a portion of the two shells forming the collector assembly.

Referring now to the drawings and more particularly to FIGS. 1 to 3, a preferred embodiment of the wet precipitator in accordance with the invention is shown housed in a metal cabinet constituted by side panels 10, a base plate 1 1 and a cover 12. The water supply for the precipitator is contained in a sliding tray 13 disposed at the bottom of the cabinet, and serving as a well. Mounted in the tray is a water pump 14, which may be electrically driven.

Vertically mounted within the cabinet is a collector assembly including a cylindrical inner collector shell 15. Concentrically disposed about the inner shell is an outer collector shell 16, an annular air passage 17 being defined between the shells. The outer shell is supported within the cabinet by means of a mounting ring 19.

Supported above the collector assembly at the top of the cabinet is a fan motor 20, the motor being positioned centrally within an inverted conical deflector 21. Positioned in the space between the deflector 21 and the collector assembly is a fan 22, the fan being attached to the shaft of motor 20. Air drawn by the fan 22 through the air passage 17 is exhausted through a set of louvered grills 23 mounted on the panels of the cabinet. Air enters the cabinet through a set of intake grills 24, the air being deflected upwardly into the air passage 17 by means of a truncated conical deflector 25.

Water sucked from tray 13 by the pump 14 is supplied through a flexible tube 26 to a water distributor 27 mounted atop the inner collector shell 15, the upper end of the shell being closed by a sealing disc 28. Water from the distributor is supplied through radially extending pipes 29 to an outer water ring 30 lying above the mounting ring 19 and provided with passages 31 which conduct the water to distribution channels formed in a circular flange 32. Flange 32 lies against the inner surface of the outer shell 16 and acts to supply water therein in a manner producing thereon an evenly distributed film of downwardly flowing water.

Water from the distributor 27 is also fed to a water ring 33 connected to the upper end of the inner shell 15 and having a passage 34 therein which supplies the water to the distribution channels formed in a circular flange 35 which lies against the outer surface of the inner shell 15 in a manner also producing an evenly distributed film of downwardly flowing water.

The structure of the water distribution flanges can best be seen in FIGS. 4, and 6 which show the circular flange 35 for the inner shell in a straight line projection. It will be seen that formed on the surface of the flange is an array of equi-spaced tapered ribs 36 which are all inclined relative to the vertical to define a series of diverging or flared water channels '37. Water enters the flange from the associated ring at the channel entrances 37a and is discharged against the surface of the collector shell at the channel exits 37b.

As best seen diagrammatically in FIG. 7, the flow of water through the divergent channels 37 causes the water at the exits thereof to fan outwardly. The diverging patterns from the various channels intersect at a point slightly beyond the exits and the resulting interference prevents build-up of the film and tends to produce an even water distribution along the collector surface. This action is further aided by the whirling motion imparted to the water by reason of the incline of the flange channels, the water thereby entering tangentially and spirally along the collector surface. The combined action of the diverging multiple streams of water and the whirling motion of the stream has been found to result in a uniform water film which adheres to the surface of the collector and avoids the presence of dry spots thereon. The flanges may in practice be made of rubber, nylon or similar material.

Attached to the lower end of inner collector shell 15 is a base ring 36 and attached thereto is a circular gutter 38A, the gutter being interposed between the upper end of conical deflector 25 and the lower end of the inner shell 15 so as to receive the downwardly flowing water therefrom. Positioned at lower end of shell 16 is an annular trough 38, the inner wall of the trough extending above and being spaced from the lower end of the outer shell 16 to receive the water flowing downwardly thereon. Suitable pipes 18 are provided (not shown) to return the water received in gutter 37 and trough 38 to the tray well 13 for recirculation. Thus continuous water films are produced in both collector shells.

Supported above the water distributor 27 and insulated therefrom is a conductive spider ring 39 from whose radially extending horizontal arms 40 are vertically suspended a group of wire precipitator or discharge electrodes 41, the wire electrodes lying midway between the inner and outer shell in the air passage 17. Pre-ionization electrodes (not shown) may be attached to the lower end of the precipitator electrodes. A suitable high-voltage power supply 42 may be housed within the space provided within the inner shell, or it may be mounted adjacent the motor 20at the top of the cabinet.

The high voltage supply is constituted by any known high voltage generator whose negative terminal is connected to the water pool and whose positive terminal is connected to the precipitator electrodes. As the water is pumped continually by the pump and allowed to fall uniformly down the collector surfaces, the potential applied to the pool by the supply will also be applied to the water films or curtains on the collectors. Thus an electrostatic field is established between the electrodes and the two fluid collector surfaces on the walls defining the annular passage 15.

The precipitator shown is capable of cleaning the air in a large enclosure, the air being drawn in through the intake grills and being conveyed through the air passage between the collector electrodes, Water sucked up from the pool is caused to flow in a tubular curtain down the collector shells, the contaminating particles being precipitated and washed down the collectors and being received in the pool. Suitable filters are provided in conjunction with the pump to prevent the return of the particles to the collectors. The air is expelled horizontally and omnidirectionally through the exit grills. It will be obvious that essentially the same system may be used for any cleaning application and the intake may be any form of contaminated gas.

In the electrode system shown in the above-noted figures, the precipitator electrodes may be provided with discharge needles or points to effect pre-ionization of the gas entering the passage. The electrodes are of relatively large diameter whereas the needles are of smaller diameter and have sharp edges to provide a sufliciently high voltage gradient to cause ionization and corona discharge. The corona discharge acts to ionize the particles, such that when they enter the electrostatic field they will be caused to migrate toward the collectors.

To eifect power economy, there is provided an electrode arrangement as shown in FIG. 8, wherein precipitator electrodes 50 supported from a ring 51 are connected to a source of direct-voltage 52 which generates a constant voltage, say in the order of 15,000 volts. Suspended below the electrodes 50 by a ring 53, and insulated from the electrodes 50, are circumferentiallyarranged corona producing discharge points 54 to which are applied periodic pulses having a magnitude in the order of 30,000 volts. The periodicity of the pulses may be in the audio range or higher.

Since the duty cycle of the pulses is relatively brief, the integrated amount of current drawn is fairly low despite the high voltage. Thus the particles in the air entering the structure are first ionized by the high potential pulses and the ionized particles are then caused to migrate by the precipitator electrodes which need not operate at so high a potential. For purposes of ionization, a constant voltage is not essential since onceionization occurs no useful purpose is served by the ionization field.

The pulse generator 55 may be of any known design,

such as is used in radar techniques, and may include differentiating networks or other pulse shaping means.

An alternative electrode structure is shown in FIG. 9, wherein the discharge electrode for creating corona effects is constituted by a series of rings 56 of relatively fine wire which girdles the group of precipitator electrodes 50. In practice, the electrodes 50 may be of a inch diameter and the rings of much finer diameter, such as 8 mil wire. The corona producing discharge points em ployed in the structure of FIG. 8 may be used in conjunction with the wire rings for increased effectiveness. In this case, the same voltage is applied to both sets of electrodes and for this purpose a DJC. supply 57 is provided which is modulated by a modulator 58 to provide pulses superimposed over a constant voltage of the DC. supply. Thus, as shown in FIG. 10, the pulses 59 are developed above the DC. level 60, the pulse peak being twice the DC. level.

In the embodiment shown in FIG. 9, the number of rings used and the spacing thereof are dependent on the velocity of the gas stream and the frequency of the high voltage pulses in the power supply. Thus, as the frequency of the high voltage pulses increases, the number of rings may be decreased, one ring being sufficient at frequencies of the order of 1000 cycles and greater. Increasing the gas handling capacity of the precipitator by increasing the velocity of the gases passing therethrough will necessitate using a larger number of rings to ensure the ionization of substantially all of the particles carried by the gas stream.

FIG. 11 depicts a schematic diagram of a high voltage pulse generator suitable for use with the precipitators herein described. High voltage supply 61 is employed to produce two D.C. voltages of different magnitudes. Supply 61 embodies a quadrupler 62 and a doubler 63 produced outputs which are related by a factor of two.

The output of doubler 62 is connected to curved contact 64. The output of quadrupler 63 is connected to curved contact 65. The inner surfaces of contacts 64 and 65 lie along an imaginary circle whose center is at point 66. Wiper 67 is rotated about point 66 by variable speed motor 68. Wiper 67 may be connected by lead wire 69 to an electrical device utilizing pulsating high voltage, such as for example the electrostatic precipitators of this invention.

The rotation of wiper 67 produces essentially a square wave voltage which fluctuates between the level of the output of the doubler 62 and the level of the output of the quadrupler 63. It is necessary to confine contacts 64 and 65 and wiper 67 in such a manner as to prevent sparking. This may be accomplished by submerging the parts in a high dielectric liquid, or, alternatively by enclosing the parts in a chamber which may be maintained at a high gas pressure.

The frequency of the output voltage is controlled by the speed of rotation of wiper 67. The duty cycle is fixed by appropriately choosing the relative circumferential lengths of contacts 64 and 65.

Other pulsating high voltage systems may also be employed in conjunction with the electrostatic precipitators of the present invention. Thus for example, instead of the contact and wiper arrangement shown in FIG. 11, either a mechanical chopper or an electronic control utillizing gas tubes as electronic gate selectors are suitable.

FIG. 12 shows a sectional view of a portion of inner collector shell 15 and outer collector shell 16. In the preferred embodiment shown in FIG. 12 the outer surface of shell 15 and the inner surface of shell 16 are coated with a porous ceramic, such as, for example, alumina. It has been determined that use of such a porous coating 70 facilitates the formation of a thin, uniform liquid film which is essential inorder to achieve high efficiency.

While there has been shown what are considered to be embodiments of the invention, it will be manifest that many changes and modifications may be made therein without departing from the essential spirit of the invention. It is intended, therefore, in the annexed claims to cover all such changes and modifications as fall within the true scope of the invention.

What is claimed is:

1. An electrostatic precipitator for cleaning contaminated gas comprising:

(a) concentrically-arranged inner and outer collector tubes defining a vertically-disposed annular gas passage,

(b) means coupled to a well to draw liquid therefrom and to feed the liquid to the upper ends of said tubes to produce a downwardly-flowing and substantially uniform liquid film on those surfaces of said inner and outer tubes which line said passage,

(0) concentrically-arranged troughs at the lower ends of said tubes to receive the downwardly-flowing liquid therefrom and to discharge the liquid into said well,

(d) inlet means to introduce said contaminated gas into the lower end of said annular passage between said troughs, said inlet means including means to admit said gas in a horizontal plane and further including a frusto-conical deflector in axial alignment with said tubes to direct contaminated gas entering in the horizontal plane upwardly through the vertically-disposed annular passage,

(e) a discharge electrode structure supported within said passage,

(f) means to apply a high voltage between said dis charge electrode structure and both of said tubes to cause migration of particles in said gas toward the films on said tubes and thereby produce a clean gas, and

(g) outlet means at the upper end of said annular passage to discharge the clean gas into the atmosphere, said outlet means including an inverted frusto-conical deflector'in axial alignment with said tubes to direct the clean gas from said passage outwardly in the horizontal plane.

'2. An electrostatic precipitator for cleaning contaminated gas comprising:

(a) concentrically-arranged inner and outer collector tubes defining a vertically-disposed annular gas passage,

(b) means coupled to a well to draw liquid therefrom and to feed the liquid to the upper ends of said tubes to produce a downwardly-flowing and substantially uniform liquid film on those surfaces of said inner and outer tubes which line said passage,

(0) concentrically-arranged troughs at the lower ends of said tubes to receive the downwardly-flowing liquid therefrom and to discharge the liquid into said well,

(d) inlet means to introduce said contaminated gas into the lower end of said annular passage between said troughs,

(e) a discharge electrode structure supported within said passage,

(f) means to apply a high voltage between said discharge electrode structure and both of said tubes to cause migration of particles in said gas toward the films on said tubes and thereby produce a clean gas,

(g) outlet means at the upper end of said annular passage to discharge the clean gas into the atmosphere, and

(h) a high-voltage supply disposed within said inner tube to produce said high voltage.

3. An electrostatic precipitator for cleaning contaminated gas comprising:

(a) concentrically-arranged inner and outer collector tubes defining a vertically-disposed annular gas passage,

(b) means coupled to a well to draw liquid therefrom and to feed the liquid to the upper ends of said tubes to produce a downwardly-flowing and substantially uniform liquid film on those surfaces of said inner 7 8 and outer tubes which line said passage, said means 1,541,678 6/1925 Bauer 55-155 to produce a downwardly-flowing liquid film on said 2,233,639 3/1941 Pegg 55-118 inner and outer tubes including a distributor flange 2,631,684 3/ 1953 Schmidt 55-119 coupled to the upper end of each tube and provided 1,377,363 5/ 1921 Moon 55-10 with diverging water channels inclined to direct water 5 1,425,637 8/ 1922 Eschholz 55-137 in a plurality of diverging streams tangentially against 2,504,858 4/ 1950 Mackenzie 55-138 X the tube surface, which streams intersect on the sur- 2,529,045 11/1950 Ortgies 261-112 X face to form said substantially uniform water film 2,696,273 12/1954 Wintermute 55-127 thereon, 1,263,941 4/1918 Schmidt 55-150 X (c) concentrically-arranged troughs at the lower ends 10 2,119,297 5/ 1938 Scott 55-6 of said tubes to receive the downwardly-flowing liquid 2,192,249 3/1940 White 55-13 therefrom and to discharge the liquid into said Well, 2,489,786 11/ 1949 Klemperer 55-138 (d) inlet means to introduce said contaminated gas into I 2,864,458 12/ 195 8 De Graaf et al 55-118 X the lower end of said annular passage between said 3,026,964 3/ 1962 Penney 55-138 X troughs, 15 2,926,749 3/ 1960 Oswald 55-108 X (e) a discharge electrode structure supported within 2,863,521 12/ 1958 Davis 261-112 X said passage, 2,896,927 7/ 1959 Nagle et al 261-112 X (if) means to apply a high voltage between said dis- 2,971,453 2/ 1961 Kinler 261-112 X charge electrode structure and both of said tubes to 977,335 11/ 1910 Shaifner 55-139 X cause migration of particles in said gas toward the 1,250,088 12/ 1917 Burns 55-118 X films on said tubes and thereby produce a clean gas, 1,357,202 10/ 1920 Nesbit 55-154 X and 1,905,993 4/1933 Buff 55-118 (g) outlet means at the upper end of said annular pas- 2,448,046 8/1948 Penney et a1. 55-118 sage to discharge the clean gas into the atmosphere. 2,615,530 10/ 1952 Hodson et a1 55-122 4. An electrostatic precipitator as set forth in claim 3, 2,863,646 12/1958 Nelson et a1 55-112 X wherein said distributor flange is provided With ribs which 1,440,887 1/ 1923 Nesbit 55-127 bear against the surface of the tube to produce said inclined water channels. FOREIGN PATENTS 858,837 12/1962 Germany. References Cited 14,771 6/ 1903 Great Britain.

UNITED STATES PATENTS gf gg- 2,937,709 5/ 1960 De Seversky. 2,351,089 6/1944 Abbey. 916,211 8/ 1951 Germany. 2,675,477 4/ 1954 Teslner DENNIS E. TALBERT, 111., Primary Examiner 2,168,402 8/ 1939 Fitzgerald 307-106 2,000,020 5/ 1935 Heinrich. US. Cl. X.R.

- 895,729 8/1908 cittrell 55-151 21 s3, 74 R; 23 2 R; 5s 129, 137, 138, 139, 148, 152, 2195431 4/1940 Shlvely 55-152 154 229 240 413 418 472- 204 312- 261-36 '11 2,412,912 12/1946 Schmidt et a1. 55-119 k 2,782,867 2/1957 Hall -139 2,888,092 5/1959 Powers 55-155

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