US 3896347 A
Description (OCR text may contain errors)
United States Patent 1191 Gelfand July 22, 1975  CORONA WIND GENERATING DEVICE 3,495,379 2/1970 Hall et al. 55/146 3,518,488 6/1970 Michalchik 3l7/4  Inventor Pele Charles Gelfand L o 3,714,762 2/1973 Fillies et a1. 55/146 73 AssigneeZ Envirotech Corporation, m 3,785,117 1/1974 Leith 55/108 Park, Calif. Primary Examiner-LL T. Hix  Flled: May 1974 Attorney, Agent, or FirmRobert E. Krebs; Thomas S.
21 Appl. 1510.; 474,625 MacDonald v 57 ABSTRACT  U.S. Cl 317/262 E; 55/108; 55/112; 1
- 55/l46 15/15 A device, whlch generates a corona wmd that CII'CU-  Int Cl B03c3/74 lates about the support rods for the emitter wires in an  Fieid 117 128 electrostatic precipitator to discourage accumulation 55 317/26 E 3 i of oil and dust particles on the insulators from which the support rodsare suspended, includes a ground  References Cited shell which spacedly surrounds the support rods and a plurality of pointed coronaemitting members that are UNITED STATES PATENTS mounted to the support rod within the shell and that 1,491,274 4/1924 Rathhun 55/146 r spatially arranged to cause the circulating gaseous 1888606 11/1932 f flow within the shell which carries entrained particulates to collection on the interior walls of the shell.
2:720:551 10/1955 W'zistvind et al. 55/146 13 Claims, 4 Drawing Figures PATENTED JUL 2 2 I975 SHEET CORONA WIND GENERATING DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corona-discharging device which is utilized to generate a comona wind and, more particularly, to sucha device for use in an electrostatic precipitator.
2. State ofthe Art Electrostatic precipitators are well-known for removing contaminating particles and droplets from gaseous streams. In large-scale industrial applications, the precipitators typically include banks of vertically extending electrodes which are disposed within a housing through which a dustladen gaseous stream is passed at relatively high velocity. The active or emitting electrodes conventionally are wires, sometimes as long as 40 feet, which hang vertically from insulators which are supported at the top of the housing. Those emitting electrodes may be charged to as much as minus 45 to 50 thousand volts. Typically, the collecting electrodes are generally flat plates which are fixedly mounted in the housing and connected to electrical ground. In operation, an electric corona discharge from the emitting wires ionize the surrounding dust particles which are then driven to the collecting plates by Couloumb force. Periodically, the collecting electrodes are vibrated or rapped so that the collected contaminants fall by gravity to the floor of the housing for subsequent removal.
Conventionally, heavy-duty ceramic insulators support the emitter wires from the roof of the housing. In practice, provisions must be made to protect those insulators from fouling by moisture, dust and mists. Accumulations of oil and tar, for example, on the insulators can cause electrical breakdown across the insulators and subsequent mechanical failure, such as fracturing. In some industrial environments, the period of critical accumulation may be as short as 2 hours. In such cases, it is common practice to purge the insulators periodically with inert gas or large quantities of steam. (In many instances, air purge cannot be used because the gas within the precipitator might explode when mixed with air, especially since electrical sparking is common in most precipitators.) Electrical heating is another method sometimes used for cleaning the insulators. As early U.S. Pat. No. 1,888,606 proposed an electric wind device for preventing foreign matter from depositing upon the electrodes.
OBJECTS OF THE INVENTION An important object of the present invention is to provide a device which minimizes the maintenance and replacement of the insulators which support the emitting electrodes of an electrostatic precipitator;
Yet another object is to provide a corona discharging device which generates a gaseous flow in such a manner as to discourage the accumulation of the oil and dust particles on the insulators which support the emitting electrodes of an electrostatic precipitator.
BRIEF DESCRIPTION OF THE DRAWINGS Further objects and advantages of the present invention may be readily ascertained by reference to the following description and appended drawings which are offered by way of example only and not in limitation of the invention, the scope of which is defined by the appended claims and equivalents. In the drawings:
FIG. 1 is a pictorial view, partially cut away to show internal parts, of a typical electrostatic precipitatorineluding devices according to the present invention;
FIG. 2 is a side sectional view, enlarged for purposes of clarity, of a portion of the precipitator of FIG. I in cluding a single one of the devices of the invention;
FIG. 3 is a side sectional view the same as FIG. 2 except that it is further enlarged to shown one of the .inventive devices;
FIG. 4 is a top sectional view of the device of FIG. 3, the section being taken along the line 4-4 in FIG. 3 for viewing in the direction indicated by the arrows.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, a conventional electrostatic precipitator includes a main housing or shell 11 that defines a flow chamber. Particulate-laden gases enter the housing at relatively high velocity through an inlet 14 which encompasses nearly the entire front wall 15 and cleaned gases leave through an opening in the rear wall. Positioned along the flow path within the housing are a plurality of emitting electrodes and collecting electrodes, all of which are vertically disposed. The emitting electrodes are long wires 19 which hand in sets from electrically conducting hanger members 21 that are disposed parallel to the direction of flow adjacent the roof 22 of the housing. Heavy tensioning weights 23 are fixed to the bottom ends of all the emitter wires so that they hang straight and do not touch the collector electrodes. The illustrated collector electrodes are spacedapart generally flat plates 25 that are fixedly supported from the housing and positioned so that their surfaces extend substantially parallel to the direction of gaseous flow. All of the collector plates are electrically grounded by the housing and, hence, are at zero voltage potential.
In practice, the emitter wires 19 are energized or charged to a high negative voltage, say minus 45 to 50,000 volts, which results in an electric field and a corona discharge between the emitter wires and the collecting plates. The corona ionizes solid particles and liquid droplets which are entrained in the gaseous stream which passes through the precipitator housing,'
and the ions are thence driven toward the collecting plates by electrostatic or Couloumb force. Periodically, the collector plates are rapped to dislodge the accumulated particles which then fall into hoppers 26 disposed in the base of the housing for subsequent removal. In many applications, such electrostatic precipitators operate at efficiencies exceeding 99 percent.
The electrically conductive hangers 21 that support the groups of emitter wires 19 are connected together in rows by electrically conductive structural beams 27 which extend transversely across the housing 11; together, the hangers and the structural beams comprise a fairly rigid support frame for the emitter wires. This support frame is, in turn, suspended by electrically conductive rods 31 which hang downward at spaced-apart intervals from the roof 22 of the housing. At their upper ends, the rods are connected to a high voltage source, not shown, which typically includes a large transformer and rectifier mounted on the roof of the housing. In the particular precipitator illustrated in FIG. 1, conventional vibration devices 28 are disposed above certain of the rods 30 to periodically shake the rods for cleaning purposes. In that case, heavy-duty insulation members 29 mechanically connect the rods 31 to the vibrators 28.
Referring now especially to FIGS. 2 and 3, the suspension rods 31 extend spacedly downward through associated relatively enlarged openings 33 that are formed inthe roof 22 of the housing. Sealingly fixed around those openings are cylindrical insulators 37 made from, for example, porcelain, fused silica or fused alumina. The rods 31 are supported from heavy metal circular plates 39 which rest on and cover the tops of the cylindrical insulators 37. The rods can be fastened to the cover plates by retaining nuts 41 or the like. Accordingly, the weight of the support rods, and hence the total weight of the emitter wires and the emitter frame, is borne by the illustrated cylindrical insulators as a compressive load. The cylindrical insulators electrically insulate the suspension rods form the precipitator shell proper. In FIG. 1, columns of the cylindrical insulators are covered by protective boxes 43 supported on the rod of the housing.
When electrostatic precipitators of the previously described design are used for cleaning gaseous streams containing certain types of contaminants, particularly light oil and tar mists, such contaminants tend to form an accumulative coating on the cylindrical insulators 37 due partially to the fact that the gaseous flow is relatively stagnant near the roof of the housing. Also, there is often gas leakage into the precipitator shell in the vicinity of the cylindrical insulators which can cause oil and dust accumulations on the insulators. In time, such accumulations may produce electrical breakdowns across the insulators and that, in turn, can cause the insulators to fracture or otherwise mechanically fail.
The present invention relates to devices, generally designated 47, for precluding or minimizing such accumulations of oil and other particles on the cylindrical insulators 37. Referring now especially to FIGS. 24, each of the illustrated devices includes a hollow electrically conductive shell 49 that has a configuration suggestive of a vertically disposed bottle or urn insofar as each shell has a wide smoothly curved midsection and narrowed ends. The shells are coaxially disposed to spacedly surround the suspension rods 31 which pass through the shells without touching the walls. The shells are electrically grounded by the precipitator housing and thus, like the collector plates, are at zero voltage potential. Preferably, the shells are fabricated from light-gauge metal.
In the preferred embodiment, both the bottom and top ends of the shells are open; which is to say that there are enlarged mouths or openings at both ends of the illustrated shells. Particularly, the bottom mouths of the shells are preferably relatively large compared to the diameter of the suspension rod 31 and those mouths are curved back slightly. In certain modifications, the top mouths of the shells may be closed or sealed. In the illustrated embodiment, however, the upper mouths of the shells are fixed to the roof 22 of the precipitator housing and surround the openings 33 through which the suspension rods pass.
'Radially extending from the support rods 31 inside the shells are a plurality of vertically disposed finshaped members, designated 51, 52, and 53 according to their size small, intermediate and large, respectively. The illustrated fins are thin plates that have a profile that resembles an apple slice, which is to say that they are nearly semi-circular. The fins are arranged in a spaced-apart series circumferentially around the suspension rods with the small fins 51 being on both sides of the larger fins 53 and on both sides of the intermediate-sized fins 52. None of the fins actually touch the shell wall 49.
The fins are electrically connected to the suspension rods, as by brazing or welding and, accordingly, are at the same high electrical potential as the emitter wires. Teeth or points 55 are formed on the outer peripheral edges of the fins and are generally directed radially and downwardly toward the bottom mouth of the shell. Preferably, the teeth are all on the edges of the fins which are situated below horizontal planes that pass through the widest or most radially extreme part of each of the fins.
Since the points are highly charged, they act as sources of electrical corona which is directed toward the bottoms of the shells. The electrical discharge, in turn, creates a corona wind within the shell. Such a corona wind is an electrical effect which relates generally to the mass flow of non-ionized gas molecules under the influence of an electrostatic field gradient. Generally speaking, corona wind is generated from highly charged point sources facing a grounded electrode; the excited ions, produced from the points, collide with'uncharged gas molecules and impart momentum to them. As a result, the air molecules are set into motion toward the grounded electrodes; such a corona wind, in fact, exerts a mechanical pressure which can be measured.
In the illustrated device, the corona wind circulates in a vortex which, as indicated by the curved arrows, is directed from the top to the bottom of the shell. More particularly, the wind circulates downward along the rod between the fins and thence upward along the walls of the shell. The pattern of the circulation is due partly to the fact that the gaseous pressure is relatively more intense immediately adjacent the discharge points 55 and, especially, in a space where there is a concentra tion of points. The shape or configuration of the shell enhances or complements the pressure gradients effected by the disposition or arrangement of the corona discharge points. Any particles or droplets entrained within the gaseous vortex, such as those which rise into the shell through the lower mouth from the precipitator chamber, will be acted upon by the forces of electrostatic precipitation and will thereby be collected on the inside walls of the shells, not on the cylindrical insulators. Usually, the oil particles which collect in the shells will drip or fall back into the electrostatic precipitator for final collection.
It should be appreciated that the illustrated shell configuration is particularly adapted to accomodate the corona wind caused by electrical discharge from the distributed points 55. In the illustrated device, for example, the radial distances from the various points 55 of the periphery of any one of the fins to the wall of the shell are generally constant. Should there be any gas leakage into the precipitator from the tops of the cylindrical insulators, the leading gases are urged, by the gas pressure distribution within the bottles, to flow along ths suspension rods rather than along the walls of the cylindrical conductors. It should also be noted that the same circulation would occur within the shells if the top mouths of the shells were sealed.
It should further be appreciated that the spatial distribution ofthe corona discharge points, and not the configuration of the fins per se, accounts for the circulating corona wind. Accordingly, it is within the scope of the invention to replace the fins with brush-like members which are constructed and arranged to provide the same spatial distrubution of corona discharging points.
l. A device for generating a corona wind comprising:
a. an electrically conductive rod-like member adapted for connection to a high-voltage source;
b. an electrically conductive shell mounted to spacedly surround said rod-like member and having a first open mouth at one end thereof through which said rod-like member passes, said first mouth being relatively large compared to the diameter of said rod-like member;
c. a plurality of thin plate-like members, each fastened on edge in a circumferential series around said rod-like member to extend outwardly therefrom toward said shell; portions of the outer peripheral edges of said plate-like members having a plurality of corona-emitting points formed thereon, said points being generally directed outwardly and toward said first mouth;
d. the surrounding wall of said shell being spaced radially apart from the peripheral edges of said platelike members, said shell being adapted for connection to an electrical ground so that electrical discharge from said points is directed toward said shell to cause a gaseous flow within said shell in the space between said shell and said rod-like member when said rod-like member is charged to a high voltage.
2. A device according to claim 1 wherein said shell has a wide midsection and narrowed ends, said midsection being formed such that the radial distances from the various points on the periphery of any one of said plates to the wall of said shell are generally constant.
3. A device according to claim 1 wherein said platelike members each have a nearly semi-circular configuration; wherein said shell has a wide midsection and narrowed ends, said midsection being formed such that the radial distances from the various points on the periphery of any one of said-plates to the wall of said shell are generally constant; and wherein said corona emitting points are arranged on the peripheral edges of said plate-like members which generally face said open mouth.
4. A device according to claim 1 wherein both ends of said shell are open and said rod-like member is disposed to pass spacedly therethrough.
5. A device according to claim 1 wherein said points are spatially distributed so that the gaseous flow circulates in a vortex within said shell, said gaseous flow passing along said rod-like member between said platelike members toward said first mouth and thence,
changes direction, and passes along the walls of said shell away fromsaid first mouth.
6. A device for generating a corona wind comprising: a. an electrically conductive rod-like member adapted for connection to a high-voltage source; 1 b. an electrically conductive shell mounted to spacedly surround said rod-like member and having a first open mouth at one end thereof through which said rod-like member passes, said first mouth being relatively large compared to the diameter of said rod-like member;
c. a plurality of corona-emitting pointed members fastened circumferentially around said rod-like member to extend outwardly therefrom toward said shell and generally toward said first mouth;
d. the surrounding wall of said shell being spaced radially apart from the ends of said pointed members said shell being adapted for connection to an electrical ground so that electrical discharge from said points is directed toward said shell to cause a gaseous flow within said shell in the space between said shell and said rod-like member when said rod-like member is charged to a high voltage.
7. A device according to claim 6 wherein said shell has a wide midsection and narrowed ends, said midsection being formed such that the radial distances from the various said points on the wall of said shell are generally constant. I
8. A device according to claim 6 wherein both ends of said shell are open and said rod-like member is disposed to pass spacedly therethrough.
9. A device according to claim 6 wherein said points are spatially distributed so that the gaseous flow circulates in a vortex within said shell, said gaseous flow passing along said rod-like member between said pointed members toward said first mouth and thence, changes direction, and passes along the walls of said shell away from said first mouth.
10. In an electrostatic precipitator having a housing through which gases pass for cleaning, a plurality of grounded collecting plates fixedly mounted in said housing and a plurality of high-voltage emitter wires suspended from conducting rods which extend below the roof of said housing, the upper ends of said rods being supported from insulators fixed to the roof inside said housing, a device for discouraging the settlement of foreign material on said insulators comprising:
a. electrically conductive shells which are mounted to surround said rod-like members and having an opening at the lower ends thereof through which said rod-like members pass;
b. a plurality of thin plate-like members, each fastened on edge in a circumferential series around each of said rod-like members to extend outwardly therefrom toward said shells; portions of the outer peripheral edges of said plate-like members having a plurality of corona-emitting points formed thereon, said points being generally directed outwardly and toward said shell opening;
c. the surrounding walls of said shells being spaced radially apart from the curved edges of said plates; said shells being adapted for connection to an electrical ground so that electrical discharge from said points is directed toward said shells to cause a gaseous flow within said shells in the spaces between said shell and said rod-like member when said rodlike member is charged to a high voltage.
11. A device according to claim 1 wherein said shells 13. A device according to claim 10 wherein said points are spatially distributed so that the gaseous flow circulates in a vortex within said shell, said gaseous flow passing along said rod-like member between said plate-like members toward said first mouth and thence, changes direction, and passes along the walls of said shell away from said first mouth.