US2349550A - Electrical precipitator - Google Patents

Description

y 23, 1944' c. w. J. HEDBERG 2,349,550

ELECTRICAL PRECIPITATOR Filed Oct. 19, 1942 Patented May 23, 1944 ELECTRICAL PBECIPI TATOR Carl W. J. Hedberg, Bound Brook. N. 8., assignor to Research Corporation, New York, N. Y., a

corporation of New York Application October 19,1942, Serial No. 482,605

Claims.

This invention has to do with an improvement in apparatus useful in electrically removing suspended particles from gases. It relates in particular to means associated with the outlet of an electrical precipitator, whereby gas after being treated in the precipitator may pass directly to atmosphere, without provision being made for hoods, exit flues, or the like, as is common practice.

While the invention may be adapted to the outlets of horizontal flow precipitators, it will be described more particularly for the purpose of illustration as part of the top header, or top header extension of a vertical precipitator. Vertical flow precipitators usually are arranged for upward flow of the gas being treated. The gas after passing through the vertical treating passages, as defined by tubular collecting electrodes for instance, is collected in a top header common to all the passages, and from the header the gas passes into a flue connected to a fan, a stack or other means, which move and direct the gas to a point of disposal. In some instances it is possible and desirable to liberate the cleaned gas, which maybe air, directly to atmosphere immediately after it is cleaned, thus eliminating the cost and space requirements of a closed top headerand exit flue and reducing the pressure required to force the gas through the precipitator. Where this has been attempted in the past, however, troublesome conditions have arisen when there was any appreciable movement of the atmosphere, (1. e. wind), across the open header. Winds set up eddies in and about an open header of usual construction, causing uneven distribution of pressure, at the exits of the treating passages of the precipitator, and uneven flow of gas through the several treating passages, respectively. The undesirable results just mentioned have prompted the building of higher headers, headers with semi-closed tops and other expedients which have required more costly and complicated construction than that ordinarily contemplated in. the use of open top headers.

The problem of maintaining the insulators of a precipitator in clean condition is made more difficult through the use or an open top header which permits turbulent flow of gas therein. In vertical flow precipitators of the type under discussion, the discharge electrodes hanging in the treating passages depend from bus bars which extend horizontaily across the top header, the bus bars being supported by insulatorshousedin compartments, or boxes, at the sides of the top header. Insulator compartments are commonly fastened directly to the header, using a side sheet of the header as an as end of an insulator compartment, and with an opening in the side sheet for the entry of the bus bar. In some preclpitators of this type, the insulator compartments are positioned at distances of from a few inches to several feet from the top header, with a horizontally extending tubular member joining each compartment to the header and serving as a housing for the bus bar that rests on the insulator 'in that particular compartment. In the use of either constrction, it is intended that the opening from the header to an insulator compartment shall be perpendicular to the flow of gas as it moves directly upwards, that is, vertically. The tendency for the gas to enter an insulator compartment and deposit such dust, fume or the like as it may carry, on the insulator in that box, thereby decreasing the dielectric strength of the insulator, is a minimum when this relationship prevails. On the other hand, it is a common ob servation that any condition in the header which disturbs the rectilinear flow of the gas in the header tends to cause eddies about and in the openings to the insulator compartments and a movement of gas into and out of the compartments, with a resulting deposition on the insulators or the particles which the gas may have carried in suspension. The top header construction comprised in the present invention, permitting operation of an electrical precipitator with the gas flowing through the top header at approximately atmospheric pressure and without turbulence, makes it possible to house the insulators in unusual manner, to be later described, which eliminates objectionable conditions commonly encountered.

It is the principal object of the present invention to provide simple and inexpensive means by which it is possible for the gas which has been cleaned in an electrical precipitator to pass directly to atmosphere relatively independent of prevailing atmospheric wind conditions.

It is a further object of the invention to provide means for maintaining desirable gas flow conditions immediately above the outlets of the treating passages in an electrical gas treater having an open top header regardless of the wind conditions at the outlet of said header.

Another object is to provide gas flow control means in the exit of an open header of an elec-' trical precipitator for the purpose of maintaining rectilinear flow of the gases in said header.

Another object of the invention is to provide protection for th high voltage insulators comprised in an electrical precipitator with an open top header in novel and useful manner.

In the following description of the invention reference will be made to the attached drawing in which:

Fig. 1 is a. plan view, partly in section, on line l-l of Fig. 2, of an electrical precipitator embodying the invention;

' Fig. 2 is a partial elevational view in partial section On line 22 of Fig. 1;

Fig. 3 is a fragmentary elevational view of a housing for a supporting insulator applicable to the precipitator illustrated in Figs. 1 and 2, and

Fig. 4 is a fragmentary elevational view of an insulator housing including an oil seal, which is comprised in one embodiment of the present invention.

Referring to Figs. 1 and 2, the numeral I identifies a top header of an electrical precipitator which includes side walls |l',-end walls l2, and a top header plate l3 to which are attached the treating ductsin this illustration, collecting electrode pipes I4. Discharge electrodes l5 depend from cross members I6 fastened to bus bar I! which in turn is supported on electrical in; sulators I8 in boxes or compartments l9. Orifice rings 20 with smooth edges of appreciable radius define holes in the side walls H of the header and spatially encircle bus bar I! where the bus bar extends through the side walls into insulator compartments l9. In Figs. 1 and 2, end walls l2 are common to header l0 and insulator compartments l9.

Header ill has an open top through which gas, after treatment in pipes M, can flow directly to atmosphere. In the header adjacent the outlet are guide vanes 22 and 23 carried, for example, on cross bars 24, for maintaining the gas in approximately straight line flow and for preventing the formation of eddies of appreciable depth by air blowing over the header outlet. The vanes, preferably, are positioned parallel to the sides of the header and to the flow of gas through the header. By positioning vanes 22 in planes perpendicular to or at a considerable angle with the planes of vanes 23, the former intersect the latter to form a structure of parallel adjacent fiues or cells, a structure which will give protection from wind coming from any direction. The crosssection and length of the fiues vary with the size and depth of the header and the severity of the atmospheric conditions prevailing or anticipated. Higher velocity and more turbulent winds require deeper fiues of smaller cross-section. In general, however, the greatest dimension of the fiues normal to the direction of the gas fiow should be substantially smaller than the depth of the header and the depth of the fiues should be at least substantially as great as the flow. Precipltators used to electrically remove acid mists fromgases are commonly made of sheet lead andvanes of thin sheet lead supported by suitable lead covered structural members provide very satisfactory construction in such precipitators.

The results which are obtained by the use of the vanes shown in Figs. 1 and 2 are indicated by.

the arrows representing gas flow in the top header and air flow in the atmosphere across the top of I the header. Solid line arrows represent the gas greatest dimension normal to the direction of gas flow. The horizontal area of the top headers of electrical precipitators may vary from a few square feet to several hundred square feet and the vertical depth of the headers will normally vary from about 6 feet to 10 feet. Assuming a header 12 feet x 18 feet x 7.5 feet high, vanes representative of the invention may be 18 inches deep, vertically, and spaced to form fiues with a cross-section 18 inches by 18 inches, although they need not be square or of rectanguler crosssection.

The vanes 22, 23 can be made of any suitable material, for instance they can be made of the same material as that of the side walls ll, l2. Corrugated sheets effectively brake the dis-, turbing eddies, although too extensive use of such shapes may add appreciable resistance to gas through the top header.

which has been treated in pipes I4 and broken line arrows represent air flow.

The small fines formed by vanes 22 and 23 divide transverse streams of air which tend to enter the top header into small streams and present considerable friction producing surface to the small streams causing them to eddy in small vortexes and dissipate much of their dynamic energy locally. The eddies extend but a short distance, if at all, below the bottom of the vanes and the result is relatively undisturbed flow of the treated gas flowing from the tops of pipes l4 some disturbance of the gas as it mixes with the eddying air just prior to leaving the header. This is, however, in striking contrast with the effect of a wind blowing across the top of an open header which has not been provided with cross vanes. The eddies are large and extend deeply. An aspirating effect is created over some of the pipes while other pipes are subjected to positive pressure which causes an actual flow of air down those pipes, making for very uneven flow of gas through the several pipes, respectively.

One of the purposes of a top header is to guide the gas away from the high voltage insulation, here indicated by post type insulators l8. But it is seldom practical in the operation of electrical precipitators to make use of solid insulation around the bus bar ll where it passes through the sidewalls of the top header into the insulator compartments. Gaseous insulation ordinarily is used as provided by the opening in the orifice rings 20. These openings permit gas to enter the compartments and dust or condensible vapors not removed from the gases in treating passages I4 will deposit on the surfaces of the insulator impairing their insulating value. If the insulator compartments are otherwise gas tight, no gas will enter except as eddies passing.into and out of the openings about the bus bar. But leaky compartments are not uncommon and when there is any considerable pressure above atmospheric in the top header considerable gas passes into and through the compartments, depositing much of the dust carried by the gas en route. Unheated insulator compartments usually are at a lower temperature than the gas being treated and if the gas comprises vapors at or near the dew points of the vapors, condensation in the compartments and upon the surfaces of the insulators is to be expected.

Fig. 3 illustrates the use of a hood 30, usually of sheet metal, to protect insulator 3| from dust and vapors that may be deposited by gas entering compartment 32 through bus bar opening 33. This is a helpful expedient for protecting insulators but it is not altogether satisfactory where acid mists and vapors are present.

The oil seal 40 shown in Fig. 4 provides a more satisfactory means of protecting an insulator against acid mists and the like. It comprises an annular pan 43 and a cylindrical member 45 with closed top. These are positioned concentrically Of course, there is about the top of insulator 42 and bus bar supporting member 44 with the bottom of cylinder 45 held between and'below the tops of the concentric annular rims of pan 43. Pan 4! is filled with insulating oil to a depth which covers the bottom of the cylinder and seals oil! the two annular passages between members 43 and 45 against the entrance of gas or air that otherwise could reach insulator 4-2. Insulator boxes usually are connected directly in gas tight relation to the top header of electrical precipitators, either by the use of a common side wall as shown in Figs. 1 and 2 or by means of a flue, connecting, for example, orifices 46 and 48 in Fig. 4. This is necessary, ordinarily, with closed top'headers operated at pressure either above or below that of the atmosphere because, if the insulator box is apart from the header with an unconfined space between, the gas will leave or air will enter through the opening about the bus bar, illustrated in Fig. 4 by orifice 48 and cause disturbing cross currents in the precipitator top header and about bus bar entrance 46 in the insulator box or compartment M. i

The improvements in top header construction already described whereby gas can be made to pass through an open top header with substantially rectilinear flow at atmospheric pressure makes possible the use of spaced apart insulator boxes without any of the disadvantages that have been associated with their use in the past. The tendency for gas to flow out or air to flow into the bus bar opening is minimized and any small amount of gas that may flow out is so diluted with air that its possible contact with the insulation is not a serious matter. Oil seals in insulator compartments directly connected to precipitators removing acid mists and conducting any corrosive fumes become contaminated making it necessary to replace or condition the oil from time to time. With an air space between insulator compartment and top header and taking advantage of the conditions provided in the present invention, the need for servicing is greatly lessened. In Fig. 4, gas flow directing plate 49 is shown mounted upon bus bar M and spaced far enough from orifice ring 49 to prevent electric discharge thereto. Its purpose is to make more positive the even fiow oigas past the opening defined by orifice E5; in header wall 58. By shaping plate it? with due regard for aerodynamic principles, (e. g. with the contours used in airplane wings) anincrease in gas velocity and corresponding decrease in pressure can be realized in the space between plate t9 and orifice 58, thus setting up a gentle inflow of air through the opening about the bus bar.

Another advantage provided by the present invention is found where precipitators are used to treat gas comprising vapors which condense or sublime upon contact with the atmosphere. If

the air sweeps deeply into the header, condensation takes place inside the header and condensate deposits on the electrode supporting structure within the header and upon the side walls of the header causing electrical short circuits and other disturbances unless properly drained away or, in the case of sublimed materials, frequently removed, mechanically. With the subdivided header, the gas is not in contact with the air nor cooled thereby until it is well out of the header and any condensate is carried away in the atmosphere.

From the above description it can be readily appreciated that the invention accomplishes the 1. In an electrical precipitator, an outlet header extending in the direction of the flow of gases from the precipitating zone of the precipitator and fully open to the atmosphere in said direction of flow, and a plurality of partition members within said header extending parallel to the direction of gas flow therein, terminating at the top of said he'ader, subdividing the crosssectional area of said header into a plurality of flues each having its greatest dimension normal to the direction of gas flow substantially smaller than the depth of said header and extending parallel to the direction of gas flow a distance at least as great as its greatest dimension normal to the direction of gas flow.

'2. In an electrical precipitator including collecting electrodes and complementary discharge electrodes suspended in spaced relation from said collecting electrodes to define a precipitating zone, an outlet header extending in the direction of the flow of gases from said precipitating zone and fully open to the atmosphere in said direction of flow, means in said outlet header for preventing the penetration of disturbances due to external wind conditions into said precipitating zone, insulator housing means positioned externally of and spaced from the walls of said precipitator, means for suspending said discharge electrodes comprising at least one horizontal member passing through a wall of said precipitator and into said insulator housing means through a zone exposed to the atmosphere external to said precipitator, and insulators in said housing means positioned to support said horizontal member.

3. In an electrical precipitator including collecting electrodes and complementary discharge electrodes suspended in spaced relation from said collecting electrodes to define a precipitating zone, an outlet header extending in the direction of the flow of gases from said precipitating zone and fully open to the atmosphere in said direction of flow, means in said outlet header for preventing the penetration of disturbances due to external wind conditions into said precipitating zone comprising a plurality of partition mem bers within said header extending parallel to the direction of gas flow therein and subdividing the cross-sectional area of said header into a plurality of flues each having its greatest dimension normal to the direction of gas flow substantially smaller than the depth of said header and extending parallel to the direction of gas flow a distance at least as great as its greatest dimension normal to the direction of gas flow, insulator housing means positioned externally of and spaced from the walls of said precipitator, means for suspending said discharge electrodes comprising at least one horizontal member passing through a wall of said precipitator and into said insulator housing means through a zone exposed to the atmosphere external to said precipitator, and an insulator in said housing means positioned to support said horizontal member.

4. An electrical precipitator comprising vertical collecting electrode surfaces, means for positioning complementary discharge electrodes in spaced relation to said collecting electrode surfaces to define a precipitating zone for the electrical cleaning of gases during upward flow trical cleaning of gases during upward flow therethrough, and gas outlet means aboye said precipitating zone comprising an outlet header having a cross-sectional area; at least as great as the cross-sectional area of said precipitating zone and fully open to the atmosphere in said direction of flow of gases therethrough and means subdividing the cross-sectional area of said header into a plurality of fines each having its greatest dimension normal to the direction of gas flow substantially smaller than the depth of said header and extending parallel to the direction of gas flow a distance at least as great as its greatest dimension normal to the direction positioning complementary discharge electrodes 15 of gas flow.

in spaced relation to said collecting electrode surfaces to define a precipitating zone for the elec- CARL W. J. HEDBERG.

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