US3917470A

US3917470A - Electrostatic precipitator

Info

Publication number: US3917470A
Application number: US398890A
Authority: US
Inventors: Pavel Xmris; Nicholas B Franco
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-09-28
Filing date: 1973-09-19
Publication date: 1975-11-04
Anticipated expiration: 1992-11-04

Abstract

An electrostatic precipitator for removing liquid and solid particles and toxic gases from an air stream in which the air to be cleansed is passed between discharge and collection electordes, and in which a glow discharge is maintained across the electrode. The glow discharge is regulated by an optical electrostatic generator, and by the geometry of the discharge electrode assembly. The optical electrostatic generator may be equipped with different discharge tubes depending upon the conductivity of the impurities in the gas. The collection electrode typically has a liquid surface. This surface facilitates the collection of the precipitated particles and the toxic gases. The liquid of the collector electrode is circulated and filtered to remove the precipitated impurities.

Description

Xmris et a1. 5] Nov. 4, 1975 ELECTROSTATIC PRECIPITATOR 2,937,709 5/1960 De Seversky 55/139 x 1 1 waik, west 2 222 31; 9122; z1:s:ii?:i-.1:; 571 Haven Conn- Q Nicholas 3,320,151 5/1967 Tepe et all. 55/139 Franco, 93 Mam Drlve, Brookfield, 3,409,409 ll/l968 Sackett, Sr 55/238 Conn. 06804 3,469,049 9/1969 Crouch et: al. 313/313 X [22] Filed: Sept. 19, 1973 FOREIGN PATENTS OR APPLICATIONS No; 149,367 12/1952 Australia 55/104 705,604 3/1954 United Kingdom 55/105 Related US. Application Data 260,566 6/1949 Switzerland 55/105 [63] Continuation of Ser. No. 76,047, Sept. 28, 1970,

abandoned. Primary Examiner-Bernard Nozick U68. 55146;55 152 [51] Int. Cl. B03c 3/08 eleCtr9Stan preclPltator for hquld i [58] Field of Search 55/118, 146 Solid Pam]? and gasesfmm an Stream WhlCh the air to be cleansed 1s passed between (115- [56] References (med gharlge and coll eition glectordifi, arlld in \/hiclhha glow isc arge 1s mam mm across e e ec ro e. e g ow UNITED STATES PATENTS discharge is regulated by an optical electrostatic gen- 1 $21 erator, and by the geometry of the discharge electrode ltney 1,976,214 10/1934 Brion et al.... 55/139 X asSe-mblfi' gg i i ir g z i 2097,233 10/1937 MeStOIl i 55/152 x eqmppe F i'. epen mg 2244 279 6/1941 Wham 55/1 51 upon the conductivity of the Impurities in the gas. The 2:305:50O 12l1942 52 X collection electrode typically a liquid surface This 2,336,625 12/1943 Milton n 55/118 surface facilitates the collection of the preclpltated 2,476,247 7/1949 Mackenzie... 317/242 particles and the toxic gases. The liquid of the collec- 2,489,786 11/1949 Klemperer.... 55/ 139 X tor electrode is circulated and filtered to remove the 2,585,777 2/1952 Hills 55/152 X precipitated impurities, 2,822,535 2/1958 Fields 55/139 2,864,458 12/1958 De Graaf et al. 55/118 x 2 Claims, 2 Drawing Figures US. Patent Nov. 4, 1975 Sheet 1 of2 3,917,470

INVENTORS PAVEL IMRIS NICHOLAS B. FRANCO BY hm) ATTORNEYS US. Patent Nov. 4, 1975 Sheet 2 of2 3,917,470

INVENTORS PAVEL IMRIS NICHOLAS B. FRANCO I ELECTROSTATIQ PRECIPITATOR This is a continuation of application Ser. No. 76,047 filed Sept. 28, 1970 now abandoned.

This invention relates to air pollution control devices and to methods purifying air and more particularly to such devices and methods which utilize a glow discharge.

Electrostatic precipitation of particles from gas streams has been studied from the beginning of this century. Various attempts have been made in the construction of these precipitators to make a practical device for air pollution control. Typically, the contaminated air is subjected to an electrical glow discharge which is maintained between a discharge electrode and a collection electrode. Extensive examination has been made of the properties of, and the behavior of, the discharge glow at various conditions of temperature, pressure gas composition, and particle (impurity) composition. Also, in the attempt to provide a more efficient precipitator, studies have been made of various shaped electrodes, and electrodes made of different materials. Presently, the discharge electrodes which have been adapted for general use, are in the shape of fine wires. The collection electrodes currently used, and which are thought to give best control over the glow discharge, include the rod curtain, the Vee plate, the expanded metal plate, and the Opzel plate. However, even with these various shaped electrodes, of different materials, it has been difficult to maintain a uniform and controlled glow discharge between the discharge and collection electrodes, with the resulting inefficient collection of particles from the gas.

Furthermore, in conventional electrostatic precipitators, it has been difficult to remove the particles from the precipitators as they are being collected, andafter they have accumulated on the collection electrode. Generally, two techniques were used to remove the precipitated particles. The first consisted of rapping or vibrating the collector electrodes. The second was to flow a liquid film over the collector electrode and wash the particles from the plate. Neither of these techniques had proved to be entirely satisfactory.

Further shortcomings of prior art electrostatic precipitators was their inability to remove a wide spectrum of different sized particles and their general inability to remove toxic gases.

The present invention overcomes the shortcomings of the prior art. It is an electrostatic precipitator having a glow discharge in which the glow is controlled by an optical electrostatic generator with longitudinal frequency. (This type of generator in described in US. Pat. No. 3,781,601 issued Dec. 25, 1973 to P. lmris and entitled Optical Generator Of An Electrostatic Field Having Longitudinal Oscillation At Light Frequencies For Use In An Electrical Circuit. The electrical glow discharge between the discharge and collection electrode is also regulated by means of changing the geometry of the discharge electrode assembly. These features provide a uniform glow discharge, and an effi' cient removal of particles from the air. By using various discharge tubes in the optical electrostatic generator, it is possible to control the conductivity in the gap between the collection and discharge electrode. Thus, if the dust particles in the air stream should have a low electrical resistivity, an optical electrostatic generator can be used which will lower the conductivity in the 2 gap. If the particles should have a high electrical resistivity, a generator can be used that will raise the con ductivity in the gap. For a gas containing a mixture of high and low resistance dust and other contaminants. a combination of optical electrostatic generators can be applied.

Another aspect of this invention is the use of an all liquid collection electrode. The electrode is typically water or water slightly acidic or slightly alkaline; however, other liquids may be used. The liquid electrode avoids the complications attendant with the various shaped solid electrodes, and the necessity of removing the precipitated particles from collection electrode. In one embodiment the liquid of the collection electrode is constantly circulating and is passed through a filter which removes the precipitated particles.

Furthermore, the liquid collection electrode of the electrostatic precipitator will remove from the air stream toxic gases such as S0 S0 NO, N0 etc.

It is an object of the present invention to provide an improved electrostatic precipitator for removing contaminants from the air and which employs an optical electrostatic generator.

It is a further object of the present invention to provide an electrostatic precipitator in which the glow discharge may be carefully regulated.

It is another object of the present invention to provide an electrostatic precipitator in which toxic gases may also be removedfrom the air stream.

It is still another object of the present invention to provide an improved electrostatic precipitator employing an optical electrostatic generator in which a liquid collection electrode is employed.

According to the invention, there is provided an electrostatic precipitator for purifying a gas comprising a discharge electrode, a collection electrode, means for guiding a gas between the electrodes, and means for maintaining a glow discharge between the electrodes, said means including a source of potential and an optical electrostatic generator connected across the electrodes.

According to the invention, there is also provided a method of purifying gases comprising the steps of generating a glow discharge in the gas to be purified and regulating the glow discharge by means of longitudinal high frequency radiation produced from an optical electrostatic generator.

The construction of illustrative embodiments a well as further objects and advantages thereof, will become apparent when read in conjunction with the accompanying drawings wherein:

FIG. 1 is a partial schematic and partial cross sectional view of an electrostatic-hydro precipitator constructed in accordance with the invention.

FIG. 2 is a partial schematic and partial cross sectional view of an alternative embodiment of the electrostatic precipitator of this invention illustrating in particular the geometry of the discharge electrode assembly.

Referring now to FIG. ll, there is shown in cross section a vessel having a bowl-shaped lower portion 1, and a flat upper portion 2. The air to be purified is drawn in at the right hand side between the upper and lower walls of the vessel, and is shown by legend 3. The cleansed air passes out at the left hand side and is shown generally by legend 4. Discharge electrodes 7 are mounted on the upper wall 2 of the vessel, extending inward and downward therefrom. The discharge electrodes 7 are shown in profile or cross section. They can be of any length extending perpendicular to the plane of the drawing; moreover, although only three electrodes are shown there can also be any number of electrodes in the precipitator. A liquid collection electrode 9 is retained in the bottom of the bowl-shaped lower portion 1 of the vessel. A glow discharge is initiated and maintained between the discharge electrodes 7 and the collection electrode 9, by means of an electrical power supply 1 1 connected across the electrodes 7 and 9. Power supply 1 I typically provides a voltage in the range of 20 to 40 kilovolts. One terminal of the power supply is connected to the liquid collection electrode 9 by a lead 12. This terminal is also grounded as shown by ground symbol 14. The other or high voltage output terminal of power supply 11 is connected by a conductor 15, through an insulating member 16 located in the upper wall 2 of the vessel, to the discharge electrodes 7. The output terminal of supply ll is also connected via lead to metal plates 17 located on the upper wall 2 of the vessel. These plates 17 assist in forming one terminus of an electrostatic field inside the vessel. The field is maintained along with the glow discharge and the plates 17 aid in stabilizing the electrostatic field against electrode 9. Shielding members 18 surround each of the plurality of discharge electrodes 7. These shielding members can be adjusted to change the geometry of the discharge electrodes assemblies and thereby control the glow discharge. Their shape, function, and operation is discussed more fully below in connection with FIG. 2.

An optical electrostatic generator 20 is connected in series with the power supply 11 in the lead 15. This generator may be of the kind shown and described in U.S. Pat. No. 3,781,601 issued Dec. 25, 1973. The generator 20 assists in the control of the glow discharge. With the addition of the generator 20 in the circuit, there is a greater separation of particles from the contaminated air thanis provided by the mere use of the conventional glow discharge (i.e., no optical electrostatic generator) associated with a high voltage across the electrodes. The optical electrostatic generator charges by an unknown radiation emitted from the alighted mass particles in the discharge tube. This radiation is effective for charging particles with diameters of 45 microns and less. The unknown radiation which can be called longitudinal high frequency radiation, is emitted by the optical electrostatic generator 20, and effectively controls the properties of the electrical discharge glow between the electrodes of the precipitator. The behavior of the discharge glow is directly proportional to the behavior of the unknown radiation. The behavior of the unknown radiation in turn is controlled by the construction of the optical generator and the gas composition and pressure of the discharge lamp in the optical generator. Details of the generator and its gas composition can be found in the above cited U.S. patent.

The unique properties of the optical electrostatic generator 20 connected in an electrostatic precipitator assist in the collection of different types of particles. If the dust particles in the air stream have high electrical resistivity, it is necessary to use an optical electrostatic generator which will increase the conductivity in the gap between the electrodes 7 and 9. If the dust particles should have low electrical resistivity, a generator can be used which will lower the conductivity in the gap.

4 For example, for highly resistant particles a Xenon lamp with relatively high pressure should be used.

For the separation of toxic gases which can be easily ionized and which can increase the concentration of ions in the electrode gap, an optical electrostatic generator which increases the resistivity of the gap and reduced the concentration of ions should be used. For such an application, an optical electrostatic generator with a high pressure mercury, cesium or sodium lamp or a low pressure neon lamp can be used. For a gas containing a mixture of high and low resistance dust and toxic gas, a combination of optical generators can be applied.

The removal of collected particulate matter is attained by circulation of the liquid, e.g., water of the collection electrode 9 through a pipe 32 and a filter 33. Circulation is effected by a pump 34. The collected toxic gases can also be removed from the water by adding suitable precipitating agents.

The air being purified flows across the surface of the water collection electrode 9, and agitates the water in constant wave motion. Thus, the gap or space between the discharge and collection electrodes is constantly varying. This variation in gap length does not affect the homogenity of the discharge glow because of the presence of the optical generator in the circuit. The presence of the water waves, moreover, is advantageous since the increased surface area means more efi'rcient absorption of toxic gases. In addition, the wave motion of electrode 9 increases the turbulence of the air passing over and this produces a more efficient impingement on and absorption of the charged solid or liquid particles in the liquid of the electrode 9.

The precipitator will also remove toxic gases from the air stream. It is believed that the mechanism for removal of toxic gases, such as S0 and N0 takes place as follows: ozone, which is generated in the electrical glow, oxidizes S0 to and oxidizes N0 to N0 which are subsequently absorbed in the water. Experiments show that if the collecting water is made alkaline, absorption of acidic toxic gases is possible.

Referring now to FIG. 2 of the drawing, there is shown in a partial schematic and partial cross sectional view, an electrostatic precipitator constructed according to an alternative embodiment of the invention. The figure also illustrates the discharge electrode assembly having a discharge electrode shield at different angles about the point of the discharge electrode. In this figure, there is shown in cross section, a discharge electrode 55 and a collection electrode 60 with the glow discharge therebetween, shown with the legend 62. The electrodes are connected by a source of power 64 connected in series with the optical electrostatic generator 66. The collection electrode 60 and one side of the power supply 64 are shown grounded at 70. Surrounding the discharge electrode 55 is a discharge electrode shield 72 made of an electrical insulating material and shown here in three different configurations. The different configurations are used to change the geometry of the discharge electrode assembly. The function of the shielding material around discharge electrode 55 is to allow control of the frequency of longitudinal oscillation between the discharge electrode 55 and the collection plate 60. Longitudinal oscillation is generated by the optical electrostatic generator 66. A change in the shape of the electrode shield 72 about the discharge electrode 55 can be detected as a change in the electrical resistance, and the concentration of ions in the gap between discharge electrode 55 and collector electrode 60. Table IV illustrated the change of electrical resistance in the gap between the discharge electrode 55 and the collector electrode 60. Measurements were taken with a single point discharge electrode 55, and with changes in the spherical angle about the discharge electrode, i.e., the angle of the shielding material about the discharge point was changed in three dimensions, with the shielding material forming a cone or spherical space angle around the discharge electrode point.

TABLE 1 SPHER POTEN- CUR- ICAL TlAL RENT POWER GAP GAP ANGLE ACROSS ACROSS ACROSS RESISTANCE LENGTH GAP GAP GAP 4: V ptA W M!) mm 24,700 50 1.23 494 45 40 25,500 50 1.27 510 45 60 26,000 50 1.30 520 45 80 26,300 50 1.31 526 45 100 26,600 50 1.33 532 45 120 26,800 50 1.34 536 45 140 27,000 50 1.35 540 45 160 27,200 50 1.36 544 45 180 27,300 50 1.36 546 45 200 28,200 50 1.41 564 45 29,800 50 1.49 596 45 220 240 32,000 50 1.60 640 45 260 35,000 50 1.75 700 45 280 39,500 50 1.97 790 45 300 50,000 50 2.50 1,000 45 B C D E F G In Table 1, column B lists the different spherical angles of the shield 72. Data is provided for shields having angles from 20 to 300. The drawing of FIG. 2 shows three different sized shields 20, 180, and 300. Column C lists the voltage applied across the gap between

electrodes

55 and 60 which is necessary to maintain a constant current of 50 microamps (column D). Column E shows the change in power across the gap with changing electrode shielding. Column F is the corresponding change in resistance across the gap, and column G shows the gap length which was held constant at 55 millimeters. The measurements for obtaining the data in Table l were made with a discharge lamp in the optical generator 66 filled with mercury vapor at 4.8 torr. Measurements were made at normal temperature and pressure with air of 40% relative humidity. If a discharge lamp was used with some other gas such as neon or zeon in place of the mercury lamp, the numerical values observed will be different from those in Table 1. However, the trends would be the same, i.e., increase gap resistance with an increase in the shielding angle. FIG. 2 and Table l illustrated the case where the shielding material surrounds a single point electrode. ln certain practical applications, however, a relatively long discharge electrode would be used, the shielding would form a constant space angle along the entire length of the electrode.

In summary, there has been shown a novel electrostatic precipitator in which a glow discharge is controlled by high frequency longitudinal oscillations from an optical generator, and in which the electrical discharge glow properties are also controlled by changing the geometry of the discharge electrode assembly. Furthermore, a liquid collection electrode was used for separating and removing contaminants from the air stream. Particles of all sizes and. many various chemical compositions of toxic gases, such as sulfur and nitrogen dioxide may be removed from the air stream. It is anticipated by combining the various technical advantages described in this invention for air purification, it is theoretically possible to remove all impurities from the air.

The above description of the invention is intended to be illustrative only, and various changes and modifications in the embodiments described may occur to those skilled in the art. These changes may be made without departing from the scope of the invention, and thus it should be apparent that the invention is not limited to the specific embodiments described or illustrated in the drawings.

What is claimed is:

1. For use in an electrostatic precipitator circuit for purifying a gas and including an optical electrostatic generator in series therewith and between said precipitator and a direct current pow-er supply, an electrode system comprising a substantially planar discharge electrode, a collection electrode longitudinally aligned with and spaced from the discharge electrode, means for guiding a gas stream between the electrodes, and power means connected to said electrodes for maintaining a glow discharge between the electrodes, said discharge electrode having at least one edge portion substantially closer to the collection electrode than the remainder of the discharge electrode, and insulator shields along the sides of said discharge electrode receding from adjacent said closer edge portion to an outer portion, said shields having a outer section which describes an are.

2. An electrostatic precipitator according to claim 11,

wherein said are is in the range of 1 to 359.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 Q'|7 .J-7O Dated November i, 1976 Inventoflg) Pavel Imris et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Title page, Item "Xmr'is" should read Imris".

Signed and Scaled this ninth Day of March1976 [SEAL] Attest:

RUTH C. MASON C. MARSHALL DANN Arresting Offizer Commissioner uj'Parents and Trademarks

Claims

1. FOR USE IN AN ELECTROSATIC CIRCUIT FOR PURIFYING A GAS AND INCLUDING AN OPTICAL ELECTROSATIC GENERATOR IN SERIES THEREWITH AND BETWEEN SAID PRECIPATOR AND A DIRECT CURRENT POWER SUPPLY, AN ELECTRODE SYSTEM COMPRISING A SUBSTANTIALLY PLANAR DISCHARGE ELECTRODE, A COLLECTION ELECTRODE LONGITUDALLY ALIGNED WITH AND SPACED FROM THE DISCHARGE ELECTRODE, MEANS FOR GUIDING A GAS STREAM BETWEEN THE ELECTRODES, AND POWER DISCHARGE BETWEEN THE ELECTRODES, SAID MAINTAINING ELECTRODE HAVING AT LEAST ONE PORTION SUBSTANDISCHARGE ELECTRODE HAVING AT LEAST ONE EDGE PORTION SUBBSTANTIALLY CLOSER TO THE COLLECTION ELECTRODE THAN THE REMAINDER OF THE DISCHARGE ELECTRODE, AND INSULATOR, SHIELDS ALONG THE SIDES OF SAID DISCHARGE ELECTRODE RECEDING FROM ADJACENT SAID CLOSER EDGE PORTION, SAID CLOSER SECTION WHICH DESCRIBES AN ARC.

2. An electrostatic precipitator according to claim 1, wherein said arc is in the range of 1* to 359*.