US3907520A

US3907520A - Electrostatic precipitating method

Info

Publication number: US3907520A
Application number: US405419A
Authority: US
Inventors: A Ben Huang; Arnold L Ducoffe
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-05-01
Filing date: 1973-10-11
Publication date: 1975-09-23
Anticipated expiration: 1992-09-23

Abstract

An electrostatic precipitating method which includes moving a gas stream with charged particles entrained therein along a prescribed path and imposing an electrostatic force field on the charged particles with a first component of force exerted on the particles opposite to the direction of movement of the particles to slow the particles down and a second component of force exerted on the particles generally normal to the path of movement of the particles to separate the particles from the gas stream.

Description

United States Patent [191 Huang et al.

[ Sept. 23, 1975 ELECTROSTATIC PRECIPITATING METHOD [76] Inventors: A. Ben Huang, 3134 Woodrow Way, NE, Atlanta, Ga. 30319; Arnold L. Ducoffe, 3544 Paces Ferry Rd., N.W., Atlanta, Ga. 30339 [22] Filed: Oct. 11, 1973 [21] Appl. No.: 405,419

Related US. Application Data [62] Division of Ser. No. 249,167, May 1, 1972, Pat. No.

[52] US. Cl. 55/4; 2l/D1G. 2; 23/260; 23/277 C; 23/284; 55/5; 55/11; 55/13;

55/114; 55/117; 55/121; 55/129; 55/131; 55/135;55/138;55/146;55/155;55/D1G. 38; 204/l57.1 R; 250/527; 250/432; 423/52;

[51] Int. CI. 803C 3/74; B03C 3/88 [58] Field of Search "SS/ 2,4, l1, 12, 13, 101, 55/108,113,114, 120,121, 131, 136, 137,

138, 154, 155, 5, 117, 129, 135, 146, DIG.

157.1 HE, 158, 158 HE; 250/527, 428, 432,

R, 55, 74 R, 74 A, 102, DIG. 2

[56] References Cited UNITED STATES PATENTS 2,225,677 12/1940 White 55/129 X m ZZ 2,249,801 7/1941 White 55/129 X 2,759,877 8/1956 Eron 208/161 X 3,370,646 2/1928 Hopper i 165/95 3,616,606 11/1971 Vincent 55/138 X 3,650,092 3/1972 Gourdine et al 310/11 X 3,681,896 8/1972 Velkoff 62/71 X 3,718,029 2/1973 Gourdine et 324/71 PC 3,733,784 5/1973 Anderson ct al. 55/341 X FOREIGN PATENTS OR APPLICATIONS 92,636 5/1923 Austria 55/131 698,874 10/1953 United Kingdom 959,655 6/1964 United Kingdom 55/131 Primary Examiner-Dennis E. Talbert, Jr. Attorney, Agent, or Firm-B. .1. Powell [57] ABSTRACT An electrostatic precipitating method which includes moving a gas stream with charged particles entrained therein along a prescribed path and imposing an electrostatic force field on the charged particles with a first component of force exerted on the particles opposite to the direction of movement of the particles to slow the particles down and a second component of force exerted on the particles generally normal to the path of movement of the particles to separate the particles from the gas stream.

7 Claims, 13 Drawing Figures US Patent Sept. 23,1975 Sheet 1 Of3 3,907,520

US Patent Sept. 23,1975 Sheet 2 01 3 US Patent Sept. 23,1975 Sheet 3 of3 3,907,520

ELECTROSTATIC PRECIPITATING METHOD CROSS-REFERENCE TO RELATED APPLICATIONS This application is a division of our copending application Ser. No. 249,167, filed May I, 1972 entitled Electrostatic Precipitating Apparatus and Method, now U.S. Pat. No. 3,782,905.

BACKGROUND OF THE INVENTION Electrostatic precipitators are available on the market today. These prior art precipitators first charge the entrained particulate matter in a gas stream and then separate the thusly charged particles by passing the gas stream with the charged particles therein through a series of charged members or grids imposed in the stream path. All of these precipitators collect the separated particles on the oppositely charged members or grids. This causes the collecting efficiency of the grids to quickly lose their collecting ability due to the insulation formed by the collected particles and requires a greater grid potential to maintain operation. Attempts have been made to solve this problem by intermittently preventing the gas stream from flowing across the grid and rapping the grid to dislodge the particles therefrom so that gravity will cause the particles to fall from the grid to be collected. This not only prevents the desirable continuous full operation of the precipitator but also does not completely clean the grid, thus reducing the effective operational time before the grids must be again rapped.

Because of the inefficiency of such prior art precipitators, attempts have been made to mechanically slow down the movement of the particles within the precipitator by creating highly turbulent zones in the gas stream within the precipitator to form eddies which entrap the particles. In order to create sufficient turbulency to significantly increase the particle collection capability ofthe precipitator, a back pressure is created requiring more power to force the gas stream through the precipitator and thus increase the cost of operating same.

SUMMARY OF THE INVENTION These and other problems and disadvantages associated with the prior art are overcome by the invention disclosed herein by providing an electrostatic precipitating apparatus and method which separates the particles from a gas stream without collecting the particles on the primary field producing grids within the stream path so that operation is continuous. Moreover, the invention creates minimum back pressure in the stream to minimize the power required to force the gas stream through the invention. Also, because the particles are not collected on the grids within the gas stream the electrical field generating power is maintained at a minimum. Moreover, the apparatus of the invention is extremely simple thereby minimizing the construction and installation cost thereof.

The apparatus of the invention includes a duct through which the gas stream is forced, charging means for charging the particulate matter in the gas stream, and separating means for separating the charged particulate matter from the gas stream. Converter means may be provided for converting gaseous pollutants into particulate pollutants for separation.

One embodiment of the separating means includes an entry grid with a charge of opposite polarity to the charge on the particulate matter and an exit grid downstream of the entry grid with a charge of like polarity to the charge on the particulate matter. At least a portion of the duct wall between the entry and exit grids is charged like the entry grid! to provide a collecting surface onto which the particulate matter is deposited. This is because an electrostatic field is generated between the entry and exit grids and the portion of the duct wall with a charge thereon which exerts a resultant force on the charged particles which has a major component of force contra to the direction of gas flow and a minor component of force normal to the direction of gas flow and toward the charged portion of the duct wall.

Additional exit grids may be spaced from each other downstream of the entry grid. The first downstream exit grid is charged to a first potential of like polarity to the charged particles, the second downstream grid is charrged to a second potential of like polarity to charged particles but higher than the first potential. the third grid is charged to a third potential of like polarity to the charged particles but higher than the second potential, etc. Thus. each exit grid has a higher potential than the next upstream exit grid to generate an electrostatic force field between each pair of adjacent grids that imposes a force on the charged particles contra to the direction of gas flow.

These and other features and advantages of the invention will become more apparent upon consideration of the following specification and accompanying drawings wherein like characters of reference designate corresponding parts throughout the several views and in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a longitudinal cross-sectional view of one embodiment of the invention;

FIG. 2 is a cross-sectional view taken along line 22 in FIG. 1;

FIG. 3 is an enlarged cross-sectional view taken along line 33 in FIG. 2;

FIG. 4 is a cross-sectional view taken along line 44 in FIG. 1;

FIG. 5 is a top view of the invention of FIG. 1 showing a wall cleaning mechanism.

FIG. 6 is a cross-sectional view taken along line 6-6 in FIG. 5;

FIG. 7 is a cross-sectional view showing a second embodiment of the separating means of the invention;

FIG. 8 is a crosssectional view taken along line 8-8 in FIG. 7;

FIG. 9 is a longitudinal cross-sectional view of a modified form of the separating means shown in FIG. 7;

FIG. 10 is a longitudinal cross-sectional view showing a third embodiment of the separating means of the invention;

FIG. 11 is a front elevational view showing an alternate form of the grid construction;

FIG. 12 is a cross-sectional view taken along line l2l2 in FIG. 11 showing modification of the grid shown in FIG. 11; and,

FIG. 13 is a free body diagram illustrating the forces on one of the entrained charged particles in the gas stream as it passes through the separating means.

These figures and the following detailed description disclose specific embodiments of the invention, however, the inventive concept is not limited thereto since it may be embodied in other forms.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS Referring to the figures, the apparatus of the invention includes generally a duct 10, a converter 11 for converting gaseous pollutants in a gas stream passing through the duct into particulate matter, a corona discharge unit 12 downstream of the converter 11 for charging the particulate matter entrained in the gas stream, and a separating section downstream of the corona discharge unit for separating the charged particulate matter from the gas stream. The first embodiment of the separating section is designated 100, the second embodiment is designated 200, the modification of the second embodiment is designated 300, and the third embodiment is designated 400.

Referring to FIG. 1, the duct 10 is illustrated with a circular cross-section but may have other configurations such as the square cross-section illustrated in FIGS. 7-9. The gas stream is forced or drawn through duct 10 by an external pumping means (not shown) as is well known in the art.

The converter 11 is placed within the passage 14 through duct 10 adjacent the entry end 15 thereof which receives the gas stream containing pollutants therein. The pollutants in the gas stream are usually in both gaseous form and in particulate form. The converter 11 converts the gaseous pollutants into a particulate form. Particulate as used herein means both solids and liquid droplets since both may be electrostatically charged for separation. While it is understood that many pollutants may be found, normally sulfur dioxide, carbon monoxide, and nitrogen oxides are found in exhaust gases in a gaseous form while carbon particles are normally found in particulate form. The converter 11 is used to convert the pollutants in gaseous form into particulate form by injecting a converting medium into the gas stream.

The converter 11 may have several configurations but is shown in FIG. 1 as a series of concentrically arranged pipes 16 located in passage 14 of duct 10 connected to a medium source 18 through a pump 19 and manifold 20. A plurality of nozzles 21 are provided on each pipe 16 for injecting the converting medium from source 18 into the gas stream entering the duct 10. While the nozzles 21 are illustrated as facing downstream, it is to be understood that they may be made to face upstream. It is also to be understood that the converting medium may be different for each gaseous pollutant to be converted and there may be a set of pipes 16 for each converting medium to be used or the converting mediums may be injected from a single set of pipes 16. Various converting mediums may be used, however, a list of possible mediums to be used are set forth in Table I hereinafter. The list of mediums shown in Table I is in no way meant to be all inclusive. Thus, thegas stream issues from the converter with all of the pollutants to be separated entrained in the gas stream as particulate matter ready for ionization.

The gas stream then passes through the corona discharge unit 12 of conventional construction. While various configurations may be used, a conventional platewire arrangement 22 is illustrated. The unit 12 may charge the particulate matter in the gas stream either positively or negatively, however, it has been found that a sufficient charge will be imposed on the particulate matter when a voltage of 20,000 volts is imposed on the plate-wire arrangement 22. Thus, the gas stream exits the corona discharge unit 12 with the particulate matter entrained therein charged.

The first embodiment of the separating section is shown in FIGS. 1-4, and includes an entry grid 101 and an exit grid 102 spaced a prescribed distance L apart. The entry grid 101 is oppositely charged with respect to the charge on the particulate matter, here shown as grounded, while the exit grid 102 is charged the same as the charge on the particulate matter. Oppositely charged or opposite polarity as used herein includes a charge with unlike polarity or grounded. Thus, while the entry grids and duct walls are illustrated herein as grounded, they could have a high voltage of unlike polarity imposed thereon. The section 104 of duct 10 between the

grids

101 and 102 has its side wall 105 oppositely charged like entry grid 101 or grounded as seen in the figures. Thus, when the

grids

101 and 102 and side wall 105 are powered, an electrostatic force field will be established between the

grids

101 and 102 and side wall 105 that will exert a force on the charged particulate matter entrained in the gas stream opposite to the direction of gas flow and normal to the direction of gas flow to separate the charged particulate matter from the gas stream and deposit same on the inside surface 107 of the side wall 105.

Referring now more specifically to FIGS. 2 and 3, the entry grid 101 includes a plurality of concentric conductor rings 106 carried on the downstream side of a plurality of radially extending circumferentially spaced support ducts 108 made of an insulating material. The rings 106 are arranged in a plane perpendicular to the path P of gas flow through the duct 10. A plurality of concentrically arranged annular ducts 109 also made of an insulating material extend between and are connected to the radial ducts 108 on the upstream side of the conductor rings 106. The annular ducts are hollow and are provided with an open mouth 110 on the downstream side thereof which is wider than the rings 106 and within which the rings 106 are positioned as seen in FIG. 3 to provide an annular opening 111 on both sides of the rings 106 which communicates with the cavity 112 within the annular duct 109. Thus, the annular ducts 109 completely cover the upstream side of the conductor rings 106 as well as the edges thereof. The rings 106 may be recessed within the annular ducts 109 to insure passage of the charged particulate matter past the conductor rings 106 before they are attracted toward the rings 106 as will become more apparent.

The internal passage in the radial ducts 108 is connected to a pressurized clean air source 114 and communlcates with the cavities 112 in the annular ducts 109 so that the clean air enters through the passage in the ducts 108, passes through the cavities 112 and is discharged around the conductor rings 106 through the annular openings 111. This further insures passage of the charged particulate matter downstream of grid 101 before they are attracted toward rings 106 as will become more apparent. The rings 106 are grounded so as to be oppositely charged with respect to the charge on the particulate matter.

As best seen in FIGS. 1 and 4, the exit grid 102 includes a plurality of annular wire rings mounted on a diametrically extending insulated support 121 so that rings 120 are concentric and lie in a plane perpendicular to the path P of the gas flow. The rings 120 are connected to a voltage source 122 so that the rings have a potential imposed thereon of the same polarity as the charge on the particulate matter. Because the side wall 105 is grounded like the rings 106, an electrostatic force field F is set up between the

grids

101 and 102 and between the grid 102 and side wall 105 which exerts a resultant forcefon each particle of the charged particulate matter which has a first major component f,. directed oppositely to the direction of gas flow to retard the downstream movement of the particle and a second component of force f which is directed radially outwardly with respect to the duct to direct the particle toward the nearest portion of the side wall 105 as will become more apparent.

Because the charged particles are deposited on the side wall 105, means may be provided for cleaning the inside surface 107 of the side wall 105 without interrupting the gas flow through the separating section 100. One specific embodiment of such a cleaning mechanism is shown in FIGS. 5 and 6 and is designated 130. Since many embodiments may be devised, this mechanism 130 is shown for illustrative purposes only. The cleaning mechanism 130 is shown in FIGS. 5 and 6 and includes a cylinder 131 which has a plurality of side walls 105 equally spaced about the center of rotation of cylinder 131 so that any one of the side walls 105 may be pivoted into registration with the rest of duct 10. The cylinder 131 is rotatably mounted by a shaft 132 adjacent the duct 10 so as to allow the side walls 105 to be selectively moved into alignment with the rest of the duct 10. An indexing motor 134 is connected to shaft 132 so as .to allow the side walls 105 to be placed in registration with the duct 10. A cleaning brush 135 driven by motor 136 is mounted on a car riage 138 diametrically opposite the duct 10 so that when the duct 10 is in registration with one of the side walls 105, the brush 135 will be in registration with another of the side walls 105. Brush 135 can be rotated by motor 136 and traversed along the carriage 138 so as to be inserted within the side wall 105 in registration therewith to clean same. Appropriate washing means (not shown) may be provided for insuring that the particulate pollutants on the inside surface of the side wall 105 will be removed as a result of the brushing action. It will also be noted that the side walls 105 are arranged closely adjacent to each other so that when the cylinder 131 is indexed by the motor 134, gas flow through the duct 10 will not be appreciably interrupted to provide for continuous operation in.-section 100.

FIGS. 7 and 8 illustrate the second embodiment 200 of the separating section. It will be understood that the second embodiment 200 will be used to replace the first embodiment 100 in the duct 10 and since the converter 11, and the corona discharge unit 12 remain the seame, they are omitted from these views for sake of simplicity. It will be noted that the duct 10 illustrated in the second embodiment 200 of the separating section has a square cross-section rather than a circular cross-section as illustrated for the first embodiment of the separating section.

The separating section 200 includes an entry grid 201 and an exit grid 202 spaced a prescribed distance L apart. The entry grid 201 is the same as the entry grid 101 for the first embodiment 100 of the separating section and is oppositely charged with respect to the charge on the particulate matter or grounded shown herein since the particulate matter has a charge of a prescribed voltage thereon. It will be noted. however, that the grid 201 has a square configuration rather than a circular configuration like the grid 101, but. the functional arrangement of the grid 201 is the same as the grid 101.

The exit grid 202 is similar to the grid 102 with a plurality of annular wire rings 220 mounted on a diametrically extending insulated support 221 so that the rings 220 are concentric with each other and lie in a plane perpendicular to the path of "the gas flow. It will be noted that the rings 221 are arranged in a configuration like the crosssection of the duct 10 and are thus in the shape ofa square as illustrated in FIGS. 7 and 8. In addition, a plurality of secondary conducting members 225 are provided along the upper edge of the grid 202 and are equally spaced from each other and from the rings 220. The members 225 are positioned on that side of the exit grid 202 toward the entry grid 201 as will become more apparent. The rings 220 and the members 225 are connected to a voltage source 222 so that the rings and members have a potential imposed thereon of the same polarity as the charge on the particulate matter.

The section 200 has a side wall 205 extending be tween the

grids

201 and 202 with a generally square tubular cross-section. The side wall 205 has an opening 206 in the bottom portion thereof under which is posi tioned a grounded collector member 230 which is insulated from side wall 205. While the collector member 230 may have any of a number of different configurations, the member 230 illustrated is a flexible conductive belt mounted on rolls 231 closely adjacent the opening 206 and lying outside of the side wall 205. A cleaning member 232 is positioned at one end of the member 230 so as to clean the deposited particulate matter therefrom as the flexible member is indexed on the rolls 231. An appropriate mechanism (not shown) is provided for indexing the member 230 periodically to selectively clean the deposited particulate matter therefrom. It is to be further understood that the side wall 205 may be insulated from the rest of the duct 10 and grounded similarly to that of section 100.

Since the member 230 is grounded, it will be seen that when the voltage of the same polarity as that on the particulate matter is imposed on the rings 220 and members 225 of the exit grid 20 2, an electrostatic force field F is set up between the

grids

201 and 202 and between the grid 202 and the grounded collecting member 230. The force field F exerts a resultant force fon each particle of the particulate-matter which has a first major componentfl. directed oppositely to the gas flow to retard the downstream movement of the particle and a second component of forcef directed downwardly perpendicular to the direction of gas flow to force the charged particle toward the collection member 230. Thus, it will be seen that the particulate matter in the gas stream will be collected on the collection member 230 and then the collection member 230 can be selectively indexed when the particulate matter collected thereon has built up to a prescribed amount. Because the particulate matter is collected on one side of the side wall 205, it will be seen that the collected particulate matter can be easily disposed of.

Referring now to FIG. 9, the modification designated 300 of the second embodiment of the separating section is illustrated. Since the converter 11 and discharge corona unit 12 remain the same, they are omitted, however, it is to be understood that they could be used in combination with this embodiment of the separating section 300. The section 300 includes generally an entry grid 301 and an exit grid 302 mounted within the side wall 305 of duct 10. It will be noted that the plane of the entry grid 301 is arranged at an angle a with respect to the path P of the gas flow in the vertical direction and perpendicular to the path P in the other direction. The exit grid 302 is arranged at an angle B with respect to the path P of the gas flow in the vertical direction and perpendicular to the path P in the other direction. The angles a and B may be varied to meet the particular requirements of each individual application.

The entry grid 301 is of the same construction as the entry grid 101 in the section 100 except that the arrangement of the insulating ducts 309 and conductor rings 306 are revised to a generally square configuration to match the square configuration of the duct illustrated and modified so that the vertical spacing between the rings 106 is equal. Likewise, the exit grid 302 is similar to the exit grid 102 of the section 100 except that the rings 302 are arranged to conform to the square configuration of the side wall 305 and that the spacing between the rings 320 are equal in a vertical plane. The bottom portion of the side wall 305 is provided with an opening 306 like the opening 206 and a collection member 330 is positioned thereunder like the member 230 so that the charged particulate matter can be collected thereon.

The entry grid 301 and the collection member 330 are connected to ground and the exit grid 302 is connected to the voltage source 332 to charge the exit grid with a potential of the same polarity as the charge on the particulate matter. Thus, it will be seen that an electrostatic force field F is established between the entry grid 301 and the exit grid 302 and the exit grid 302 and the collection member 330 so that a resultant force fis imposed on the charged particles of the particulate matter within the section 300 which has a first component fi. directed oppositely to the direction of gas flow and a second component f,, which is directed downwardly toward the collection member 330 normal to the path P of the gas flow. Therefore, the charged particles of the particulate matter entering the section 300 will be displaced downwardly and onto the collection member 330 to separate the particulate matter from the gas stream. The collection member 330 may be indexed as specified for the separating section 200 to remove the collected particulate matter therefrom.

The third embodiment 400 of the separating section is illustrated in FIG. 10. In this embodiment, an entry grid 401 is provided and a plurality of exit grids 402 are also provided. While any number of exit grids may be used in the section 400, three are illustrated and are designated 402,,, 402,, and 402,.. The

grids

401 and 402 are arranged so as to lie in a plane perpendicular to the direction of the gas flow with the entry grid 401 having the same configuration as the entry grid 101 because the side wall 405 is of a circular cross-section. Likewise, each of the

exit grids

402,,402,. have a configuration similar to the configuration of the exit grid 102 of the first embodiment 100 of the separating section. The exit grid 402,, is spaced a prescribed distance L from the entry grid 401, the exit grid 402,, is spaced a prescribed distance L from the exit grid 402,, and the exit grid 402, is spaced a prescribed distance L" from the exit grid 402,,. While various distances L, L or L may be used, they are illustrated as equal in FIG. 10, it being understood that these distnaces are dependent upon the diameter d of the duct 10. The entry grid 401 is grounded as with the other embodiments of the invention, the exit grid 402,, is charged to a first potential V, of the same polarity as the charge on the particulate matter, the second exit grid 402,, is charged to a second potential V which is greater than the potential V on the grid 402,,. The next exit grid 402, is charged to a potential V which is greater than the potential V on the grid 402,,. Thus, there will be a first force field F set up between the entry grid 401 and the first exit grid 402,, which exerts a resultant component of forcefon each particle of the charged particulate matter which is directed oppositely to the direction of the gas flow. Likewise, a second electrostatic force field F will be set up between the

grids

402,, and 402,, which also exerts a component forcef, on the particles of the particulate matter which is opposite to the direction of the gas flow. Also, an electrostatic force field F will be set up between the

grids

402, and 402,. that exerts a component of force f on the particles of the particulate matter which is directed oppositely to the direction of the gas flow. Thus, as the particulate matter progresses through the section 400, the particles have a force exerted thereon which is constantly and oppositely directed to the direction of the gas flow. Because there is a natural self-repulsoin force between the particles of the particulate matter as a result of all of the particles having like charges thereon, this self-repulsion force will tend to displace the particles toward the side walls within the section 400 thus separating them on the side wall 405 as the particles move through the section 400. To further enhance the separation of the particles from the gas stream. the side wall 405 may be grounded as illustrated for the other embodiments of the separating section to cause the particles to be deposited thereon. Likewise, the

grids

401 and 402 may be arranged to cause the particles to be separated in a single downwardly direction as illustrated in FIGS. 7-9.

Referring to FIGS. '11 and 12, an alternate embodiment of the entry and exit grids is illustrated and designated 500. The grid 500 is a plate 501 having a configuration corresponding to the cross-sectional configuration of duct 10 having a plurality of punched openings 502 therethrough to leave narrow ribs 504 in place 501. To allow use of the grid 500 as an entry grid a thin insulating coating 505 of known material may be used to cover the upstream facing side of plate 501 and the edges of the openings 502 as seen in FIG. 1. To make an exit grid, the coating 505 is omitted. The grid S00 is substituted for the grids described hereinbefore and serves the same function.

OPERATION In operation, it will be seen that the polluted gas stream is forced or drawn through the duct 10 along the path P. If the polluted gas stream contains gaseous pollutants as is generally the case with exhaust gases, the stream first passes through the converter 11. The converting medium is injected into the gas stream whereupon the medium reacts with the gaseeous pollutants to form particles. Because different mediums may be used for each type of gaseous pollutant or for different pollutants, it is to be understood that more than one injection unit, here shown as pipes 16 and nozzles 21, may be necessary to obtain conversion of all of the gaseous pollutants. Also because the converting medium itself may be in a gaseous, liquid or solid state, it may be necessary to modify the converter to inject the particular medium. However, it is to be understood that such modification is within the scope of the invention.

When the gas stream is exhaust gases from a power source such as factory or electrical power plants or in ternal combustion engines, the converting medium may be selected from those identified in Table I attached hereinafter.

For example, sulfur dioxide (S may be converted into solid particulate matter by injecting ammonia (NH from nozzles 21 or injecting calcium oxide (CaG) or maganese dioxide (MnO in powder form through nozzles 21. Heating coils HC may be placed in duct to assist in heating the gas stream for better reaction. The nitrogen dioxide (N0 may be converted into an aerosol containing both liquids and solids by injecting one of the cyclic olefin compounds such as ethylene from nozzles 21. An ultraviolet source US, here shown as a sun lamp but may be a mercury arc, may be provided for enhancing the reaction speed. The nitric oxide (NO) can first be converted to nitrogen dioxide by the injection or air or oxygen (0 and then converted as above described.

Carbon monoxide, on the other hand, can be converted into harmless carbon dioxide (CO by the injection of air or oxygen (0 as is well known especially if the gas stream is heated by coils HC. Also, the carbon monoxide can be converted by injecting lead chloride combined with water PbCl H O with the lead being removed by the separating sections. It must also be noted that converter 11 may not be necessary if only particulate matter already in the gas stream is to be removed.

After the gas stream exits the converter 11 it enters the corona discharge unit 12 as it moves along path P in duct 10. The unit 12 operates in known manner to charge the particles in the gas stream to a predetermined level with a particular polarity. The plate-wire arrangement 22 has either the plate or wire grounded in conventional manner with either a positive or negative polarity potential imposed on the ungrounded plate or wire. Thus if a positive polarity potential is imposed thereon, it will be seen that the particles passing therethrough while entrained in the gas stream will have a resulting positive charge imposed thereon while a negative polarity potential will impose a negative charge on the particles.

It is also to be understood that some of the particles within the gas stream may more readily accept a charge thereon of either a positive polarity or negative polarity. If such is the case, it may be necessary to have a first corona discharge unit 12 for imposing a charge on the particles of one polarity and the gas stream passed through the

separating section

100, 200, 300 or 400 to separate those particles which have accepted a charge. The gas stream can thereafter be passed through a second corona discharge unit 12 to impose a charge on the remaining particles of the other polarity and the gas stream passed through a

second separating section

100, 200, 300 or 400 to separate the remaining particles.

Referring to the free body diagram as best seen in FIG. 13 of a particular charged particle P, of the particulate pollutant matter in the gas stream as it issues from the corona discharge unit 12, it will be seen that the gas stream exerts a force F on the particle Pp due to its entrainment gene ally parallel to the path P of movement of the gas stream through the duct 10. This path P is horizontal as seen in the figures. however, it is to be understood that path P could be at other positions such as vertical. Also forces F will be exerted on the particle Pp by the self-repulsion between particles due to their charges of like polarity. Because the outside layer of particles Pp adjacent the side wall of the duct 10 has no repulsion with respect to the side wall. there will tend to be a general drift of the particles Pp toward the side wall. There will also be a gravitational force FM acting on the particle P however, such force is generally insignificant in the operation of the invention.

When the particle P, passes within the first embodiment of the separating section, it passes between the annular ducts 109 as indicated by phantom lines in FIG. 3 and is deflected past the grounded conductor rings 106 by the clean air shown in dashed lines in FIG. 3 issusing through the openings 111 on both sides of the rings 106. The particle Pp is now located within the side wall and is acted on by the electrostatic force field F between the

grids

101 and 102 and side wall 105. It will be noted in FIG. 1 that side wall 105 is insulated from the rest of the duct 10 at I. Thus, as seen in FIG. 13, the force field F will exert a resultant force fon the particle Pp. The force fhas one componentfl. which is diametrically opposite to the force P of the gas stream on the particle. The componentf serves to retard the movement of the particle P along the path of movement P. The forcef also has a component f, generally perpendicular to the path of movement P. The component f, is directed radially outward from the path of movement P so that the particle P, will be deflected outwardly toward the nearest portion of side wall 105. This deflection is seen by the phantom lines in FIG. 1. Thus, the particles Pp will be deflected toward and collected on the inside surface 107 of side wall 105 in an outwardly flaring funnel shaped pattern. It will also be noted that the contra component f,. is the major component of force fand the radial componentf, is the minor component since the major part of the electrostatic force is used to slow down the particle so that it can be easily separated.

The distance L between the entry grid 101 and exit grid 102 may be varied for the optimum separating efficiency. The distance L will depend on the diameter d of duct 10. Also, the potential difference between the entry and

exit grids

101 and 102 and between the exit grid 102 and side wall 105 may be varied to obtain maximum separation. It has been found, however, that a potential difference of 10,000 to 40,000 volts between

grids

101 and 102 and between grid 102 and side wall 105 is sufficient. In practice, the potential difference is maintained as high as possible without arcing. Of course it is to be understood that additional sections 100 may be placed downstream of the section 100 illustrated to remove any particles from the gas stream that were not removed in the first section 100. Also, it will be noted that the electrostatic field F acts as a means for charging the particles P Thus, in some cases, the corona discharge unit 12 may not be necessary where the particles will be both charged with a charge of a polarity like grid 102, especially if the grid 101 is grounded, and separated from the gas stream after the charge is imposed thereon.

When the cleaning mechanism 130 is used, the cylinder 131 is positioned to align one of the side walls 105 in the duct so that the particulate matter will be collected on the inside surface 107 of the aligned wall 105. When the surface 107 of the aligned side wall 105 becomes coated with particulate matter to such an extent to affect the collecting efficiency thereof, the cylinder 131 is indexed by motor 134 until the next side wall 105 is aligned with the duct 10 without interrupting the operating of the section 100. When the coated side wall 105 is indexed to the cleaning brush 135, it is rotated by motor 136 and moved along carriage 138 to clean the side wall 105. Thus, it will be seen that the operation is continuous.

In the operation of the second embodiment 200 of the separating section, the particles P pass the grid 201 in the same manner as described for grid 101. The electrostatic force field F will exert the force fon the particle P with the componentf, diametrically opposite the force F thereon in the same manner as the force f,. of field F to retard the movement of the particle along-path P. The component f,, of force fas seen in FIG. 7 corresponds to force f, of field F in that it is directed normal to path P, however, it is different in that it is directed only toward the collection member 230 completely across the crosssection of the side wall 205. Thus, the particles within section 200 will be deflected toward the collection member 230 across the entire cross section of side wall 205 as indicated by phantom lines in FIG. 7.

When the collection member 230 has been sufficiently coated with the collected particulate matter to lose its collecting efficiency, the member 230 is indexed to place a clean portion thereof in registration with the opening 206 in the side wall 205 to provide for continuous operation while the cleaning member 232 cleans the coated portion of member 230. While only one member 230 is illustrated, it is to be understood that additional members 230 may be positioned around the side wall 205 and in combination with additional members 225 on exit grid 202 on that side of the passage 214 of side wall 205 opposite the additional collection members 230 to also separate the particles from the gas stream. It is also to be understood that different types of cleaning mechanisms and collection members may be used in lieu of those illustrated.

The operation of the modification 300 of the second embodiment of the invention is virtually the same as the second embodiment thereof. Because the angles a and B for

grids

301 and 302 are selected in the range of 45 to 90, the componentf, of force fretards movement of the particles Pp while the component f,, of force fdeflects all of the particles toward the collecting member 330 as indicated by phantom lines in FIG. 9. It will be noted that the plane of the charged surfaces of

grids

301 and 302 define the included acute angles a and ,8 with the plane of the surface of the collection member 330 exposed to the gas stream and intersect the plane of the collection member along a line normal to the longitudinal centerline of the member 330 which is parallel to the path P along which the gas stream passes. Also, the exit grid 302 extends over the member 330 from the downstream end thereof.

As seen in FIG. 10, the particle Pp passes through the entry grid 401 of the third embodiment 400 of the separating section in the same manner as it passes grid 101 in the first embodiment 100. Because the side wall 405 is grounded, the particles are subjected to the same forces f, and f as they move between

grids

401 and 402,, as described for the first embodiment of the separating section to be collected on side wall 405 between

grids

401 and 402,,, the side wall 405 being insulated from the rest of the duct 10 at l.

[f the particle Pp is not separated in the field F between

grids

401 and 402 it passes downstream of grid 402,,. Unlike the first embodiment 100 wherein the charged particle would be speeded up when it passed downstream of the exit grid 102, however, it encounters the electrostatic field F to exert the force f thereon with the contra component f,. and the radial componentf, seen in FIG. 10 which causes the particle to continue to slow down while at the same time continue to be deflected outwardly toward the grounded side wall 405 between

grids

402,, and 402,,. It will be noted that side wall 405 is also insulated from the rest of duct 10 at the insulators l. The electrostatic field F, will be generated as long as the potential on grid 402,, is greater than that on grid 402,, and of the same polarity as grid 402,, and the charge on the particles. The side wall 405' is charged with a polarity opposite to that of grid 402,, here shown as grounded, to continue to attract the particle theretoward and collect same thereon.

Likewise, if the particle Pp is not separated from the gas stream in the field F, between

grids

402,, and 402,,, it passes downstream of grid 402,, to be subjected to the electrostatic field F between

grids

402,, and 402,. Because the potential imposed on grid 402,. is always greater than that on grid 402,, and of the same polarity as the potential on grid 402,, and the particles Pp, the forcef, exerted on the particle Pp has a componentf," contra to the flow of the gas stream and a component f, in a radial direction with respect to the side wall 405" and normal to the path P. The side wall 405" is also grounded and insulated from the rest of duct 10 at l"v This insures that the particles will continue to be attracted toward the side wall 405'.

It is to be fuurther understood that while only three grids 402 are illustrated in FIG. 10, additional grids 402 may be placed downstream of those illustrated with "each having a higher potential imposed thereon than the adjacent upstream grid 402 with the same polarity as the adjacent upstream grid 402 to generate a repulsive force field. While different voltages V,, V and V may be used depending on the particular kind of particles to be separated and the desired separating efficiency, one set of suggested voltages is 10,000 volts f0 voltage V,, 20,000 volts for voltage V and 30,000 volts for voltage V,,. As discussed with the first embodiment 100 of the separating section, the distances L, L and L" between grids 401 and 402,402, may be varied for maximum separating efficiency and will depend on the diameter d of the passage defined by

side walls

405, 405 and 405'.

In some applications, the grid 401 may not be necessary with all of the separation taking place between the

grids

402,,402,. If such is the case, grid 401 can be eliminated and the side wall 405 need not be grounded.

It is also to be understood that in some instances the

side walls

405, 405 and 405" may not need be oppositely charged or grounded. This is because the self repulsion forces between the particles will cause them to drift toward the side walls as they are slowed down by the contra forces from force fields F, F and F of the duct wall between the first and second grids; imposing an electrical potential ofa prescribed value on the second grid with the same polarity as that on the particles to generate an electrostatic repulsive The difference between the operation of a precipita- 5 force field between the second grid, the first grid tor using a series of separating sections 100 and the and the duct wall which exerts a first component of separating section 400 is that each time a particle force on the particles as they pass between the first moves downstream of an exit grid 102, it is accelerated and second grids opposite to the direction of move until it passesthe next downstream entry grid 101 ment of the gas stream along the prescribed path whereas a retarding force is constantly exerted on'th'e l and exerts a second component of force on the parparticle from the time it enters the section'400 until the ticles generally toward the duct wall and normal to time it leaves the section. This results in reducing 'the the movement of the gas stream to slow the movesection 400 to a minimum by maximizing the separatment of the particles with the gas stream and deing efficiency thereof. fleet the particles to the duct wall for collection;

With the invention disclosed herein, the less turbul and, lent the flow of the gas stream through the duct the preventing the collection of the charged particles on better the separating efficiency. Thus, the sections'of the upstream side of the grounded first grid so that the invention are designed to introduce a'minimum of the particles are collected only on the duct wall. turbulence into the gas stream unlike those prior art 2. Themethod of claim 1 wherein the step of preprecipitators which use turbulence to mechanically venting the collection of the charged particles on the slow down the particles. This results in maintaining the upstream side of the grounded first grid includes elecpumping power necessary to force the gas stream trically shielding the upstream. side of the first grid. through the precipitator at a minimum. 3. The method of claim 2 wherein the step of pre- The use of grid 500 in lieu of the grids previously ilventing the collection of charged particles on the uplustrated does not materially change the operation as stream side of the grounded first grid further includes above described. It will be noted that the coating 505 directing a secondary stream. of a gaseous medium may be necessary when grid 500 is used in lieu of the without charged particles therein around the

peripheral entry grids

101, 201, 301 or 401 to prevent collection edges of the first grid to cause the gas stream with the of the particles thereon. charged particles therein to bypass the grounded first While specific embodiments of the invention have grid without the charged particles being collected on been disclosed herein, it is to be understood that full the first grid. use may be made of modifications, substitutions and 4. A method of separating charged particles from a equivalents without departing from the scope of the ingas stream including the steps of: ventive t, 3 moving the gas stream with the charged particles en- TABLE I GASEOUS POLLUTANT To BE CONVERTING ME- PARTICULATE PRODUCT DIUM CoNvERTED MEDlUM STATE PRODUCT STATE Sulfur Dioxide Ammonia Gus Ammonium Sulfate Solid (S01) (NHH) l( il-z il Sulfur Dioxide Calcium Oxide Solid Calcium Sulfate Solid (S02) (CaO) (CaSO,) Sulfur Dioxide Manganese Di- Solid Manganese Sul- Solid (SO. oxide (MnO fate (MnSO,) Nitrogen Dioxide Cyclic Olefin Gas Aerosol Liquid/Gas (NO- l Group Nitric Oxide Air/Ox gen Gas Nitrogen Di- Gas (NO) (O2) oxide (N02) Carbon Monoxide Air/Oxygen Gas None 1 (0 Carbon Monoxide Lead Chloride Solid Lead Solid (CO) (PbCl H2O) We claim: trained therein along a prescribed path within a tu- 1. A method of separating charged particles from a b la d t; gas stream including the steps of: positioning a plurality of first open grids so as to inmoving lhC gas stream with [llC charged particles entcrsect said prescribed path spaced from each trained therein along a prescribed path through a other b a ib d di tubular duct; imposing an electrical potential ofa prescribed value positioning a first open grid within the tubular duct on said most upstream first open grid with the same so that the first grid extends generally transversely polarity as that of the charge on said particles;

across the prescribed path; imposing an electrical potential on the remaining first positioning a second open grid within the tubular grids of the same polarity as the charge on said parduct a prescribed distance downstream of the first ticles, the charge on each of said remaining first grid so that the second grid extends generally transversely across the prescribed path; electrically grounding the first grid and that portion grids having a value a predetermined amount greater than the charge on the next adjacent upstream first grid;

positioning an additional second open grid so as to intersect said prescribed path and spaced upstream from said most upstream first open grid.

electrically grounding said additional second open grid and said tubular duct between adjacent open grids; and,

electrically shielding the upstream side of said second open grid to prevent the collection of the charged particles thereon so that an electrostatic repulsive force field is generated between adjacent grids and the duct wall therebetween which exerts a first component of force on the particles as they pass between adjacent grids opposite to the direction of movement of the gas stream along the prescribed path and exerts a second component of force on the particles generally toward the duct wall and normal to the prescribed path to slow the movement of the particles with the gas stream and de' fleet the particles to the duct wall for collection.

5. The method of claim 4 further including the step of directing a flow of a gaseous medium without charged particles therein about the peripheral surfaces of said second open grid and generally parallel to the prescribed path to cause the gas stream with the charged particles entrained therein to pass by the second open grid without particles being collected thereon.

6. The method of claim 5 further including the step of imposing a charge on the particles entrained in the gas stream upstream of said second open grid of the same polarity as the charge on said first grids.

7. The method of claim 6 further including the step of injecting a converting medium into the gas stream upstream of the point at which the electrical charge is imposed on the particles therein to convert gaseous pollutants in the gas stream into particulate matter for acceptance of an electrical charge thereon.

Claims

1. A METHOD OF SEPARATING CHARGED PARTICLES FROM A GAS STREAM INCLUDING THE STEPS OF: MOVING THE GAS STREAM WITH THE CHARGED PRTICLES ENTRAINED THEREIN ALONG A PRESCRIBED PATH THROUGH A TUBULAR DUCT POSITIONING A FIRST OPEN GRID WITHIN THE TUBULAR DUCT SO THAT THE FIRST GRID EXTENDS GENERALLY TRANSVERSELY ACROSS THE PRESCRIBED PATH, POSITIONING A SECOND OPEN GRID WITHIN THE TUBULAR DUCT A PRESCRIBED DISTANCE DOWNSTREAM OF THE FIRST GRID SO THAT THE SECOND GRID EXTENDS GENERALLY TRANSVERSELY ACROSS THE PRESCRIBED PATH, ELECTRICALLY GROUNDING THE FIRST AND THAT PORTION OF THE DUCT WALL BETWEEN THE FIRST AND SECOND GRIDS, IMPOSING AN ELECTRICAL POTENTIAL OF A PRESCRIBED VALUE ON THE SECOND GRID WITH THE SAME POLARITY AS THAT ON THE PARTICLES

2. The method of claim 1 wherein the step of preventing the collection of the charged particles on the upstream side of the grounded first grid includes electrically shielding the upstream side of the first grid.

3. The method of claim 2 wherein the step of preventing the collection of charged particles on the upstream side of the grounded first grid further includes directing a secondary stream of a gaseous medium without charged particles therein around the peripheral edges of the first grid to cause the gas stream with the charged particles therein to bypass the grounded first grid without the charged particles being collected on the first grid.

4. A method of separating charged particles from a gas stream including the steps of: moving the gas stream with the charged particles entrained therein along a prescribed path within a tubular duct; positioning a plurality of first open grids so as to intersect said prescribed path spaced from each other by a prescribed distance; imposing an electrical potential of a prescribed value on said most upstream first open grid with the same polarity as that of the charge on said particles; imposing an electrical potential on the remaining first grids of the same polarity as the charge on said particles, the charge on each of said remaining first grids having a value a predetermined amount greater than the charge on the next adjacent upstream first grid; positioning an additional second open grid so as to intersect said prescribed path and spaced upstream from said most upstream first open grid, electrically grounding said additional second open grid and said tubular duct between adjacent open grids; and, electrically shielding the upstream side of said second open grid to prevent the collection of the charged particles thereon so that an electrostatic repulsive force field is generated between adjacent grids and the duct wall therebetween which exerts a first component of force on the particles as they pass between adjacent grids opposite to the direction of movement of the gas stream along the prescribed path and exerts a second component of force on the particles generally toward the duct wall and normal to the prescribed path to slow the movement of the particles with the gas stream and deflect the particles to the duct wall for collection.