US2700429A

US2700429A - Electrical precipitator

Info

Publication number: US2700429A
Application number: US314802A
Authority: US
Inventors: Harry A Wintermute
Original assignee: Research Corp
Current assignee: Research Corp
Priority date: 1952-10-15
Filing date: 1952-10-15
Publication date: 1955-01-25
Anticipated expiration: 1972-01-25

Description

J n- 2 19 H. A. WINTERMUTE ELECTRICAL PRECIPITATOR 4 Sheets-Sheet 1 Filed Oct. 15, 1952 ATTORNEY Jan. 25, 1955 H. A. WINTERMUTE 2,700,429

ELECTRICAL PRECIPITATOR Filed Oct. 15, 1952 I 4 Sheets-Sheet 2 INVENTOR HARRY A. WINTERMUTE ATTORNEY Jan. 25, 1955 H. A. WINTERMUTE 2,700,429

ELECTRICAL. PRECIFITATOR Filed on. 15, 1952 4 Sheets-Sheet :5

INVENTOR HARRY A.WINTER MUTE ATTORNEY Jan. 1955 H. A. WINTERMUTE 2,700,429

ELECTRICAL PRECIPITATOR Filed Oct. 15, 1952 4 Sheets-Sheet 4 INVENTOR HARRY A.W|NTERMUTE ATTORNEY United States Patent ELECTRICAL PRECIPITATOR Harry A. Wintermute, Plainfield, N. 1., assignor to Research Corporation, New York, N. Y,, a corporation of New York Application October 15, 1952, Serial No. 314,802

8 Claims. (Cl. 183-7) This invention relates to the electrical precipitation of suspended materials such as dust, smoke particles and carboniferous particles, from bodies of gas in which they are suspended. It has been found that many types of present precipitators have a much lower eificiency when treating coarse and carboniferous particles than when handling particles of finer fractions. The difficulty of retaining such coarse and carboniferous particles on a collecting electrode plate depends, to a considerable extent, upon the velocity of the gases which are being treated. If the gas velocity is reasonably high, then it is quite difiicult to collect the particles. Particular diificulty is encountered when the coarse particles contain a large proportion of coked material, which is often found to be the case in many common installations. Some of the reasons these particles are difiicult to collect are:

1. They do not agglomerate readily with other particles.

2. Their relatively large areas give them considerable sail effect.

3. The coked or carboniferous particles charge and discharge readily. Therefore, they bounce up and down along the surface of the collecting electrode, and this property together with their sail effect causes them to dance along the surface and out of a precipitator unless collected by trapping them in a pocket or receiving hopper.

It is a principal object of the present invention to provide a method and apparatus for overcoming the above ditficulty. This is accomplished according to the invention by causing the gases bearing the particles to pass through a system of precipitating electrodes so arranged that not only will the gases be caused to follow a tortuous path in the precipitating field, but also their velocity will be greatly reduced in this area. The tortuous path is so arranged that the gases tend to be moved in a direction which will favor collection of the particles while the gases move in a different direction. Furthermore, the cross-sectional area of the path of motion of the gases in the precipitating field is effectively larger in the vicinity of the collecting electrode than it is in the vicinity of the discharge electrodes, thereby rendering the collecting electrode effective to precipitate even the larger particles of the type above referred to. Also, the collecting electrodes are so arranged in a vertical plane that particles reaching them either fall into a hopper below the electrodes by gravity or are caught by traps which are arranged in the direction of motion of the particles, but not of the major portion of the gas. Thus the particle is caught in one of these two ways, and cannot easily escape.

The specific nature of the invention, as well as other objects and advantages thereof, will clearly appear from a description of a preferred embodiment as shown in the accompanying drawings in which:

Fig. l is a sectional plan view taken on line 11 of Fig. 3 of one form of precipitator according to the invention;

Pig. 2 is a side elevation, partly in section, of the precipitator and its housing;

Fig. 3 is a sectional front view taken on line 3-3 of Fig. 2;

Fig. 4 represents an expanded perspective view of the discharge and collector electrodes, respectively, of the modification of the invention disclosed in Fig. 1;

Fig. 5 is a perspective view of a different form of= "ice discharge electrode from that shown in Fig. 1, and adapted to be substituted therefor;

Fig. 6 is a schematic sectional view of the electrodes including the discharge electrode shown in Fig. 5, with a mechanical rectifier shown at the supply source;

Fig. 7 is a view similar to Fig. 6, except that the discharge electrode is of the form shown in Fig. 1, and an electronic discharge type of rectifier is shown instead of a mechanical rectifier.

Referring to Fig. l, the precipitator is shown housed in a shell or casing 1, which may be inserted in a duct 31 through which the gases to be treated are passing. Discharge electrodes 2 and collector electrodes 3 are suitably supported within the housing by means Which will be described in detail below. Collector electrodes 3 are in the form of extended surface members formed of screen material, perforated sheet material or expanded metal so as to provide a large number of perforations through which the gas and suspended material may readily pass. in a plurality of V-shaped configurations as clearly shown in'Fig. 1 and Fig. 5, and have no sharp points on the surface so that they will not give a corona discharge toward the opposite discharge electrode members 2. The discharge members 2 may be formed as a series of louver-shaped members struck out of a single sheet of metal as best shown in Fig. 4, or, alternatively, may be constructed of a number of metal angle members to be held together by plate or angle members 26. Although only two of these members 26 are shown for each angle member, one at the top and one at the bottom, it will be apparent that one or more intermediate members may be provided for additional strength if desired. The edges of the discharge electrodes may be serrated as shown at 2e to provide corona discharge points where desired. Since the discharge electrode members extend parallel to the collecting electrodes, it will be apparent that they will, in general, converge toward each other in the downstream direction. At the convergent end of each electrode structure is placed a precipitate or grit trap for collecting precipitated particles, particularly the larger particles which may have been unable to adhere to the collecting electrodes 3, for the reasons described above, and which are therefore carried generally downstream along the collecting electrodes until they are accumulated by traps 4. A pipe 5, best shown in Figs. 1 and 2, is provided for collecting the precipitate and gas in which the particles are suspended from trap 4. This is intended for installations with which an auxiliary collector is used and may be dispensed with under most circumstances. However, in some installations, the use of such a collecting pipe and auxiliary collector may be found necessary. Individual legs 6 are run from the collector pipe 5 to the traps 4. The pipes are so dimensioned and arranged that uniform gas pressure is provided in each trap 4 to insure even gas distribution for transporting the collected material, or alternatively, a damper may be supplied to each of the legs 6.

Supporting members 7 are provided at the gas inlet end for stiifening the collector electrodes, and additional stiffening bar supports 8 may be used for maintaining uniform spacing between the opposing electrodes. At the bottom of the precipitator housing a dust receiver hopper is provided. The electrode construction, as can be seen from the drawings, is open at the bottom and most of the finer precipitate will fall by gravity from the electrodes into this hopper. The usual vibration means, not shown, will be employed to facilitate this action. A screw or drag conveyor may be provided at the bottom of the hopper for removing the collected material. If desired, a gas vacuum system can be used instead.

Baflle member 11a is connected to an electrical contact with the grounded electrode members 2. Since this baffle extends upwardly in some places above the bottoms of the grounded electrodes 3 the bafile members are cut away, as shown at 11c, to provide electrical clearance distance from the high potential electrodes 3. Baffle member 11b is connected to and in contact with the high potential electrode 3. The grounded electrode 2 is there- The collector electrodes are arranged fore cut away as shown at 2a in Figs. 2 and 4 to provide electrical clearance between this baffle, which is at high tension, and the grounded electrode 2. Bafiie 12a is provided for closing off the area above the precipitating zone and a similar baffle 12b is provided downstream at the precipitator outlet for preventing gas sneakage above the electrodes after the gases enter the precipitating zone. A third baffle 120 may be provided midway between the gas inlet and outlet for preventing gas sneakage above the precipitating zone. This baflie extends from the roof plate down to the grounded electrode member. In order to do this, a cut-out 12d, sufiicient to give electrical clear ance, is supplied at the top of the high potential electrodes. A horizontal baffle 13 is provided at the bottom of the precipitator inlet for preventing gases from entering the hopper Zone, and a corresponding bafiie 14 is located downstream to prevent gas sneakage through the hopper.

At the top of the precipitator housing are provided additional bus housings 15 for protecting the insulator and other high tension members, one such housing being shown for each set of transversely disposed insulators 16. These insulators both insulate and support the weight of the high-tension electrodes 3 by means of vertical support members 18 which are both electrically and mechanically fastened to electrode 3 by means of angle members 19 as shown, and are electrically connected at the top of insulator to high voltage lead 22 which passes through insulating bushing 21, and is connected to the usual high voltage source. An orifice ring 20 is provided through which the vertical bars 18 pass, thus insuring adequate clearance to the grounded casing of the precipitator housing. The ground connection to the housing is indicated at 24, and a suitable high voltage lead is connected to the ground side of the electrodes at 23, this lead running to the other side of the high voltage source to which lead 22 is connected.

No electrode cleaning means have been shown. It will be. understood by those skilled in the art that means such as vibrators can be attached to each of the banks of discharge electrodes at the lower bars 26 in the modification of Figs. and 6 or the lower portion of the discharge electrode 2 in the modification of Fig. 2. A cross bar can also be attached to the tops of the high tension electrodes, which in turn is attached to a vibrator through an insulating means. All this is well understood in the art and therefore in the interest of clarity is omitted from the drawing.

As best shown in Fig. 6, the dust-laden gas passing downstream along duct 31, after passing through high tension electrode 3, is caused to curve sharply back upon itself and thus follow a tortuous path as indicated by the arrows. The sharp backard turn is, of course, accomplished much more easily by the light gas molecules than by the relatively heavy suspended particles, especially those of larger size, which tend to be flung out in the direction shown by the smaller arrows 28. At the same time, these particles, when passing in the vicinity of the grounded discharge electrodes 2 acquire a charge in the usual fashion which also tends to cause them to move in the electrostatic field back toward the perforated high tension electrode 3. The combination of both of these forces is effective where the electrostatic field alone would not be in the case of larger particles to attract most of them toward high tension electrode 3. Even such particles as are not definitely attractedso as to cling to the collector electrode 3 will be moved by the downstream component of the gas current in the vicinity of electrode 3 toward its downstream apex. At this point, if the particles become separated from the collector electrode, it will be apparent that they are now in a low gas velocity region, and can readily be caught by trap 4 in which the particles now find themselves. If collector tube 5 is employed, the low-velocity gas containing a high concentration of large size particles will move down pipe 6 to pipe 5 for complete precipitation in another stage, the gas now being at a sufficiently low velocity to make this easily possible. For many types of installation this will not be found necessary and the precipitate can be successfully trapped at 4 to fall into the bottom of the dust-receiving hopper 9 from which it may be suitably conveyed by a screw or drag conveyor- It will be noted in Fig. 6 that the cross section available for gas flow at the base or outlet side. of grounded electrode 21 issmaller than near the. discharge. points. Thus it will. be.- seen that in this modification, the velocity of the gas is necessarily greater near the broadened base of the grounded discharge electrode 2 than near the point thereof, due to the inherent shape of the orifices provided by the series of discharge electrodes. This effect still further tends to decrease the velocity of the gas in the critical region near the discharge points, and thus make the electrical field still more effective in acting upon the larger particles. In the modification shown in Figs. 1 and 7 this effect is not as great, since the apertures provided at 2c by the cut-out portions of the sheet from which the louvers 2d are struck provide almost as great a cross section available for gas flow as is found in the region near the discharge points of the electrodes. However, this effect is somewhat compensated for by the fact that the angle of reversal is even sharper in this modification than in that of Fig. 6, and this sharp reversal of the gas flow tends to be very effective in exerting centrifugal force on the particles to. prevent them from freely following the course of the gas flow, and tends to move them down toward the apex 3a of the high tension electrode 3. Figs. 6 and 7 also show respectively, by way of example only, the use of a mechanical rectifier 34 or an electronic discharge device 35 for which purpose Kenetron rectifiers have been successfully employed.

It will be noted that the shape and arrangement of the precipitator electrodes themselves are utilized to change the path of current gas flow in such a manner as to enhance the effect produced by the electrical discharge between these electrodes. This had been found to be very effective in removing a range of particles including larger sizes which have heretofore required an additional mechanical removal step.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

I claim:

1. Electrical precipitator apparatus comprising a gas passage, aperturedcollector electrode means disposed across said gas passage so as to require dust-laden gas from. said passage to pass through the apertures of said electrode means, discharge electrode means downstream from and opposite to said collector electrode means, said discharge electrode means comprising a plurality of louver- ]ike discharge electrodes having a series of sharp loci disposedin a surface parallel to said collector electrodes to define a discharge field between said opposed electrodes, said discharge electrode means being substantially parallel to each other and set at such an angle relative to said collector electrode surface as to define a series of re-entrant gas passages between adjacent ones of said discharge electrodes for sharply changing the direction of flow of gas from the apertures of the collector electrode while said gas is in the discharge field between the electrodes.

2. The invention according to claim 1 including mechanical. particle trap means located adjacent said precipitator electrodes ina direction opposite said direction of flow through said louver-like discharge electrodes, whereby dust particles which cannot follow the sharp change in direction of the gas in said discharge field are caught by said trapmeans.

3. The invention according to claim 2, said trap means being downstream of said collector electrodes, said collector electrodes being vertically disposed, and additional hopper means disposed below said collector electrodes for receiving particles by gravity from said collector means.

4. The invention defined in claim 2, said apertured electrode means comprising two substantially planar perforated electrode members arranged in the form of a 1 with the apex pointing downstream, said trap means being located near the apex of said V'.

5. The invention according to claim 3 including flue means in. said trap means for collecting a concentrated mixture of gas at low velocity and dust particles from said trap. means.

6. The invention according to claim 1, each of said louver-like discharge electrodesv being wedge-shaped with the base downstream and the sharpened edge constituting the discharge: electrode; lecus.

7, The? invention. defined in; claim 6, said sharpened 5 6 edge being serrated to constitute a series of discharge Refgrences Cited in the file of this patent points.

8. The invention defined in claim 1, each of said UNITED STATES PATENTS louver-like discharge elements being slat-shaped and c0m- 2,357,734 Hafer Sept. 5, 1941 prising adjacent slats struck out of a single sheet of con- 5 FOREIGN PATENTS ducting material.

545,605 Germany Mar. 3, 1932