US2347709A - Electrical dust precipitator - Google Patents

Description

M y 2, 1944- I r G. w. PENNEY 2,347,709

ELECTRICAL DUST PRECIPITATOR Filed March 12, 1941 2 Sheets-Sheet 1 j'nsub/v 'an WITNESSES:

13 KIM M14? INVENTOR GO u/MvAZ/QHhey ATTORNEY- Patented May 2, 1944 ELECTRICAL DUST-PRECIPITA'IOR Gaylord w. Penney, Wilkinsburg, Pa., assigndr to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 12, 1941, Serial No. 382,852

13 Claims.

This application is a continuation-in-part of my application, Serial No. 321,457, filed February 29, 1940, and assigned to the Westinghouse Electric & Manufacturing Company.

It is a broad object of my invention to provide an electrical precipitator of the type having precipitator-electrodes or plates paralleling the gas-flow, which will be more compact and considerably smaller than prior devices of the same type with the same equivalent rating.

It is an important object of my invention to provide an electrical precipitator of the type described adapted to clean air to be breathed, which is of such high capacity, compared to its size, which is relatively small, that the application of such electrical precipitators to transportation means such as railway trains, buses, and the like, becomes for the first time commercially attractive and practical.

Precipitators of the type. to which my inven-- tion relates follow, to some'extent, the general teachings of my Patent No. 2,129,783, granted September 13, 1938, and assigned to the Westinghouse Electric & Manufacturing Company. such precipitators are especially useful for removing duct particles from an air-stream, by dust particles, or equivalent expressions, meaning any foreign particulate matter carried in the air and capable of being removed by electrostatic means.

However, in the preferred embodiment of my invention the cleaning operations for removing the dust from the flowing gases are divided into three separate stages or zones, rather than two separate stages or zones such as previously employed. The three zones. of this embodiment comprise successively in the path of the gas-flow: an ionizing zone, an initial precipitating zone, and a final precipitating zone. Additionally, washing means is employed for occasionally washing the parts forming one or'more of these zones. In another embodiment the initial precipitating zone is omitted.

It is a primary object of my invention to prosulated relation by a plurality of small insulating spacer devices distributed over the surfaces of facing plate-electrodes so that a plurality of closely spaced plate-electrodes canbe utflized in an electrostatic precipitator with an assurance that the plate-electrodes will be maintained properly spaced, even though they might have some flexibility. This close spacing shortens the deflection-path of charged particles, enabling an increased gas-flow velocity or shorter plate-electrodes in the gas-flow direction, or both, without increased flashovers or increased power drain.

However, in known devices, the minimum distance between precipitator-plates is limited by vide a device of the type described having a final precipitating zone which has plate-electrodes paralleling the gas-flow, in which the electrodes are relatively very closely spaced in the order of as little as three-sixteenths to one-eighth of an inch, or less, betweenelectrodes of opposite polarity as compared to minimum spacing of from onefourth to five-sixteenths of an inch, which represents the closest spacing attained previously in commercially-utilizable devices of the prior art.

It is a general object of my invention to provide plate-electrodes which are kept in spaced inpractical difflculties and considerations arising out of the building and use, as such, of the precipitator, and such spacing between flat or bent parallel plates or other shapes of precipitatorplates of one-fourth to five-sixteenths of an inch represents about lowest limit in spacing which was used, to the best of my knowledge, in devices of the prior art.

In accordance with a preferred form of my invention, I provide an initial precipitating zone with relatively widely spaced precipitator-electrodes for collecting the larger-sized dust particles, while permitting the smaller-sized particles to pass through it; and subsequently providing a final precipitating zone of closely spaced precipitator-plates for collecting the smaller particles, the closely spaced precipitator-plates being held in spaced relation by a plurality of spacers at a number of points distributed over the surface of each of them. These precipitator-plates can be thinner than, and need not be as accurately shaped as, those heretofore used which were supported only at their ends with no intermediate means to maintain their spacing, thereby requiring greater thickness or strength to provide the necessary rigidity to support their own weight, and to withstand undue bending or deflection caused by the gas-flow forces, or the electrostatic forces, or similar forces tending to defiect the electrodes and make them vibrate.

I consider the use of spacers distributed over the precipitator-electrodes a highly novel and important feature of invention since the spacers keep the precipitator-electrodes in definite spaced relation at the spacer points and prevent excessive deflections of the precipitator-electrodes between spacer points, keeping possible irregularities in spacing within tolerable limits.

All factors entering into my invention permit me to produce an electrical precipitator which is considerably smaller than previous imits of the An important aspect of my invention resides in the provision of an electrical precipitator having an initial ionizing zone and a separate precipitating zone following the ionizing zone in the direction of gas-flow, which preclpitator is of small overall size but of larger cleaning capacity so that it can be used in a situation where large cleaning capacity is required but where the space available for afllxing or adding the precipitator is extremely limited. A railway car is a specific example of such a situation. For such and similar uses it is desirable to coat the plates with a film of a liquid which will cause the precipitated dust to adhere or stick to the plates,

so that higher gas-velocities can be used without danger of dirt blow-oil," and to wash the accumulated dirt from the plates at intervals. Both washing and coating can'be accomplished in one operation by using a suitable viscous liquid, hereinafter embracively designated as oil, as the washing liquid, there being enough oil adhering to the plates after a washing and drainage to provide the adhesive film. However, to limit the size of the preclpitator, and to permit it to be relatively permanently attached to a vehicle, the oil is not stored or contained in the preclpitator but attachments are provided enabling oil to be pumped through the precipitator from a portable oil container having a pumping mechanism. By this means a few portable containers attachable and detachable from the precipitator can service a great many precipitators,

the portable containers being located, in the instance of railway use, at suitable terminal or servicing way stations.

Further objects, features, methods and combinations of my invention will become apparent from the following description thereof, which is to be taken in conjunction with the drawings on varying scales.

In the drawings Figure l is a symbolic, vertical sectional view of a preferred embodiment of my invention utilizing precipitator electrodes in the form of fiat precipitator-plates;

Fig. 2 is a similar fragmentary view showing a modification iri which the intermediate zone,

that is, the initial precipitating zone, has been omitted;

Figs. 3 through 5 are views collectively showing, in a schematic way, the required elements for a preferred embodiment of a final zone precipitating meanshaving fiat closely spaced pre-. cipitator-plates. In these figures: Fig. 3 is an elevational view, on a decreased scale, of one plate of the insulated or high potential series; Fig. 4 is an elevational view, on a decreased scale, of one plate of the second or grounded series; Fig. 5 is a fragmentary, vertical sectional view,

on an enlarged scale, showing the manner in which the plates are assembled and held in A spaced relation;

Fig. 6 is a top plan view of a casing in which the closely-spaced preclpitator-plates are supported, the plates being omitted for clarity of illustration;

Fig. 'I i an end elevational view thereof, with .a part in section;

Figs. 8 and 9 are, respectively, enlarged fragmentary views in elevation and section of a detail of construction utilizable for clamping the spacers and preclpitator-plates together;

Fig. 10 is an elevational view, on a somewhat decreased scale, of a high potential plate of the first precipitating zone, having combined therewith the supporting means for an ionizing wire of the ionizing zone;

Fig. 11 is a schematic wiring diagram of a scheme of electrical connections for energizing the precipitator device;

Figs. 12 and 13 are schematic vertical sectional viws, on section planes transverse to each other, of a modified form of my invention for horizontal gas-flow. .A unit of this kind is particularly adapted for railway use, and has a built-in structure for distributing oil over one or more of the zones of the preclpitator for washing and coating the precipitator-electrodes; and

Fig. 14 is a curve of breakdown voltage gradient in kilovolts per inch as ordinates against electrode spacing in fractions of an inch as abscissae, for closely spaced large diameter spheres. 4

Referring more especially to the modification shown in Fig. 1, the preclpitator unit comprises an outer metallic casing or housing 2 having an inlet flange 4 defining an inlet opening 6 at its bottom, and an outlet flange 8 defining a discharge opening 18 at the top of the casing. An inlet conduit 12 can be secured to the fiange 3, and an outlet conduit [4 can be secured to the outlet flange 8, the conduits forming part of any suitable air-conditioning or ventilating system, or even may be open where the unit is to a be used alone. A motor I8, which may be anyany suitable manner by one skilled in the art in accordance with the teachings of this invention. The initial ionizing zone A comprises spaced tubular non-discharging ground electrodes 20 transverse to the gas-flow betweenrwhich are dis-.

posed ionizing wires 22, the number, arrangement and size of these elements being determined in accordance with the teachings of my aforesaid patent. Preferably, the ionizing wires are less than 32 mils in diameter for precipitators used for cleaning air. The initial precipitating zone B follows the ionizing zone in the direction of gasflow, and comprises a plurality of high potential non-discharging precipitator-electrodes in the form of plates 24 suitably supported on two or more narrow metallic connecting bars 28 in turn supported from spaced insulators 28 depending from a narrow metallic supporting bar 38 secured to sides of the casing 2. The plates 24 are spaced in relation to the iuxtaposedparallel sides of the cured or made integral with the intermediate ground electrode 20 of the ionizing means.

The ionizing wires 22 may be supported in insulated relation to the ground electrodes 20 in any suitable manner but I prefer to support them directly from the plates 24 in the manner shown in Fig. 10, each of the corners of the plates 24 which are toward the ionizing zone being provided with end brackets 34 between which an ionizing wire is strung. A structure of this kind is shown and claimed in my copending, application Serial No. 319,079, filed February 15, 1940, which matured into Patent 2,255,677 of September 9, 1941. An intermediate bracket 36 may be used to support the wire intermediate its ends. The brackets are metallic and preferably extend beyond the lower edge of a plate 24 a distance sumcient to take the ionizing wire out of its shielding eflect on the ionized field created by the wire. To avoid point discharges which may be a source of ozone-production, the ends of the brackets are rounded. I am able to so support the ionizing wires in direct conductive relation to the plates 24 for the reason that the plates of the first precipitating zone are relatively widely spaced and, consequently, a high voltage may be connected across the plates oi opposite polarity,

. that is, the grounded plate-electrodes on the one hand and the plates 24 on the other. The spacing is deliberately chosen to require a voltag approximately the same as that required between an ionizing wire 22 and its cooperating ground electrode 20. In the instant embodiment a spacing of from one and three-fourths .to two inches between the plates of the initial precipitating zone has been found adequate and will efiectively remove substantially all the large-sized particles contained in the usual air-stream, while permitting smaller-sized particles to pass through to the second and final precipitating zone C symbolicallyindicated, in Fig. 1, above the supporting bar 30.

This final precipitating zone comprises a plurality of closely spaced non-discharging precipitator-electrodes in the form of plates which are alternately insulated anduninsulated so that in effect, the plates can be divided into two series;

plates 40 comprising one series, and the plates The plates of one series,

42 the second series. for example, the plates 40, are grounded and preferably electrically connected one to another and to one terminal of a source of power, and the plates 42 are similarly electrically connected one to another and to an opposite terminal of the source of power. The three zones A, B and C of my novel precipitator merge one into another and are compactly arranged, but are preferably disposed in the housing 2 to provide suiiicient space above and below them for a uniform distribution and flow of the gases through the zones. If desired, or necessary, the customary baifles ratus.

may be employed to direct ancl'guide the gasa flow to and from the precipitating apparatus. In order to conveniently distinguish the widelyspaced precipitator-electrodes from the closelyspaced precipitetor-electrodes, I hereinafter refer to them as precipitator-electrodes and plateelectrodes, respectively; utilizing the terms plates, electrodes, or precipitator-plates generally for either or both. according to the context.

An oil-washing means forms a part of this embodiment, and to this end the bottom of the casing 2.1.! provided with a reservoir 44 adapted to hold a volume of oil which may be pumped, by means of a pump 46 driven by .a motor 48, from the reservoir through a pipe system to a distributing nozzle 50 from which the oil is discharged in all directions to wash the accumulating dirt from the precipitating apparatus, the dirt settling in the reservoir 44 from which it may be drained through a hole closed by a drain plug 52. or otherwise removed.

In an actual embodiment of my invention, the precipitating plates 40 and 42 may be spaced as close as three-sixteenths to one-eighth of an inch apart, and somewhat less, between adjacent surfaces and consequently a low voltage source may be connected across the two series of plates without decreasing the potential gradient between them below the value required for the precipitation of the dust particles from the gas-stream at a given gas-flow velocity. As a matter of fact; for a commercially-acceptable eillciency, I have found that a voltage source of as low as 2500 volts is sufllcient between plate-electrodes having an extent of approximately six and one-half inches in the direction of a gas-flow having a velocity of approximately 600 to 750 feet per minute; and with lesser velocities, the voltage can be decreased still further. However, I prefer to use somewhat higher voltages.

The operation of the precipitator shown in Fig. 1 is obvious to one skilled in the art. The gases flowing into the casing 2 first pass through the ionizing zone A in which the gas-borne dust particles are electrically charged. The first precipitating zone B has high potential plates energized by a 12,000-1-3,000 direct current voltage source, which are approximately five inches long in the direction of gas-flow for conditions previously described; and the large-sized particles are collected in this zone. although, of course, some of the small-sized particles which pass close to the proper plates may also be drawn to them. However, the large-sized particles with their larger charges will be deflected toward the plates of the first precipitating zone so that there is little, if any, possibility of clogging or shorting of the plates of the second precipitating zone C where the charged small-sized particles are collected.

The oil-washing system isv preferably operated occasionally and while the precipitating unit is deenergized. To this end I have shown in Fig. 11 a schematic wiring diagram in which the conventional household voltage supply 54 energizes the motors-I6 and 48 and alimited-energy voltage conversion power pack 56, constructed in accordance with the teachings of my aforesaid Patent No. 2,129,783. This power pack converts the household alternating-current voltage to the necessary unidirectional voltages to be applied to the difierent elements of the precipitating appa- A three-position swltch58, which may be either manual or time-controlled, in its upper position energizes the power pack 56 and the motor l6. in its intermediate position deenergizes potential plates 24 of the precipitating zone B by means oi an insulated conductor I'+. Since the A precipitator built in accordance with the above teachings actually can be designed to cocupy a cubical space of almost one-half that of the minimum sized precipitators for cleaning air of the prior art and having the same rating. Moreover, a' precipitator of the type described will have as high an efllciency and will be rugged and durable in use, because clogging and frequent flashovers between the precipitator-plates are substantially eliminated. By intermittently washing the precipitating apparatus, all the parts can be kept relatively clean and can be maintained oil-coated so that the dust particles will adhere and stick to the precipitating-plates. Consequently, such a precipitator may be employed for cleaning gases containing a large variety of kinds and sizes of dust particles. In instances where the dust particles contained in the gas are all relatively small, it is possible to elimihate the intermediate zone B, and Fig. 2 is a symbolic representation of such a precipitator. In this embodiment the precipitator unit comprises only the ionizing zone A and the precipitating zone C' of closely spaced plates, similar to the zones A and C, respectively, of the first embodiment. The ionizing wires of zone A may be supported by selected ground electrodes 28, as shown in E. H. R. Pegg Patent No. 2,215,298, granted September 17, 1940.

The use of close spacing between precipitatorplates is a highly desirable feature in itself and may be used with either fiat plates or bent plates.

Consequently, a specific construction for a precipitating means with closely spaced precipitatorplates is shown in Figs. 3 through 9.

As applied to the specific embodiments disclosed, one plate of one series of plates, preferably the insulated plates 42, as shown in Fig. 3, comprises essentially a rectangular plate whose long dimension transverse to the direction of airflow is determined by the number of cubic feet per minute that is to flow through a completed unit, and whose short dimension in the direction of gas-flow is determined by the gas velocity.

to a considerable extent, this corner being the corner aligned with the corners of the high potential plates 42 having the apertures ID. This permits the connecting wire between these apertures to sag to'some extent without contactin the ground plates or seriously disturbing the air insulation between the wire and ground plates. An aperture I4 may also be provided in the upper corner, which may be considered an ear or lug, of the plate 48 opposite a cut away corner of the plate 42, by means of which the ground plates may be positively electrically connected together by a wire I8 (Figs. 2 and 13) in a manner described for the high potential plates.

The plates of each series are somewhat similar in contour and each is provided with a plurality of holes I6 distributed over their surfaces, in the particular embodiment being arranged staggered in spaced horizontal rows. These holes are used to position and align spacers which maintain the adjacent precipitator-plates in insulated spaced relation, and a relatively large number of these holes are distributed over the surfaces of the precipitator-plates so that they will be accurately spaced and located with respect to each other, thereby enabling a thinner gauge metal to be used, as compared to the gauge of precipitatorplates positioned by other means, as, for example, by slotted bars such as described in my aforesaid patent.

As shown in Figs. 3 and 4, three horizontal rows of holes I6 are provided in each precipitatorplate, the top and bottom rows containing three holes, and the middle row two holes staggered with respect to the holes of the outer rows.

The spacers employed for maintaining the precipitator-plates in spaced relation are shown more particularly in Fig. 5. The spacers are symmetrical and are formed of a ceramic or semiceramic material, or any other suitable insulating material having very high resistivity. Each spacer I8 is solid and shaped with a pair of parallel, annular surfaces 88 and 82 adapted to abut the facing surfaces of a pair of adjacent plates 48 and 42. Concentric with the surface 88, the spacer is provided with a central projection 84 which fits a hole I6. This projection 84 i is rather narrow, but is slightly longer than the The plate has three of its corners cut oil as shown, a fourth comer, which may be considered an ear or lug, being provided with a slot or an aperture Iilthrough which a wire may be passed electrically connecting all the plates of this series in any suitable manner, such as, for example, by soldering or welding the wire to the plates where it passes through the different slots or apertures.

One plate of the other series of plates, preferably the ground plates 48, is shown in Fig. 4, and also comprises a substantially rectangular plate somewhat wider and longer than the plates 42 so that when the precipitator-plates are assembled together in a manner to be shortly described, the peripheral edges or boundaries of the insulated plates 42 will be air insulated from the grounded housing in which the precipitatorplates are supported. As may beobserved in Fig. 4, one of the cornersof each plate 40 is cut away thickness of a plate to provide a portion which may fit into and engage a suitably formed aligned slightly larger cylindrical groove 86 centrally of the surface 82 of the next successive spacer.

Consequently in assembling the precipitatorplates, one plate 48 of one series may be laid horizontally with projections 84 of spacers I8 in each of the holes I6 of the plate. A second plate 42 may be similarly assembled with its spacers and then placed over the first assembly, with the projections 84 of the upper assembly mating the grooves 86 of the lower assembly. In this way the entire precipitating means may be assembled with plates 40 alternating with plates 42.

It is highly desirable to limit the energy consumption by the precipitating zone including the precipitator-plates; and consequently, the spacer devicesare so formed that any current-leakage them'to provide transverse curved ring surfaces 0. Consequently, it may be observed that each spacer is in effect asolid of revolution whose con. tour is formed by rotating the outline shown in Fig. about an axis indicated at .82. However, the maximum diameters of such spacers arerelatively small, in the order of %f' or less, with the outer diameter of the surfaces 00 and 02 being about of an inch. The spacers are preferably glazed.

The assembled plate-electrodes and spacers can be mounted in a casing indicated in its entirety by the reference numeral 94. Referring to Figs. 6-9, this casing comprises an bpen-ended box-.- like member having three of its sides permanently secured together and the fourth side removably secured thereto. Ihe three permanently secured sides are indicated at 90, 98 and I00, the first two of which are similar to each other and the third of which is secured across the ends of the first two. The side I00 is preferably provided with edge flanges I02 and I04 for rigidity and strength, the flanges I02 preferably being welded to the edges of the sides 88 and 98. A side I06 is adapted to be secured to the other edges of the sides 00 and 98 and is similar in construction to the side I 00 having flanges I00 and H0 similar to the-holes I0. The insulated spacers for the last spaces between the plates would preferably be provided with two central projections.

' Such casing units can be made in standard sizes, and the required number arranged side by side to fill a suitable air-flow conduit or housing. In a practical embodiment, -each of such units has about 13 closely spaced air-paths for each air-path between an ionizing wire and cooperating curved ground electrode, but this number is illustrative only. By supporting the insulated plates on spacers as described, I avoid the use of relatively large bars and insulators disposed outside the boundaries of the precipitator-plate assembly for supporting the plates. The means for conducting energizing potential to the inv sulated plates comprises only a wire which is supported by such plates and is disposed within the boundaries of the precipitator-plate assembly.

Figs. 12 and 13 show a further modified form of my invention for a substantially horizontal airflow, which can clean a large volume of air, but which has very small overall dimensions, an

- actual embodiment having a housing with a width the flanges I02 and I04 of the side I00. However, the flanges I 08 and II 0 are provided with a plurality of slots II: elongated in a direction toward the side I00.

Each of the sides I00 and I06 are provided with a pair of holes at their tops and bottoms through which extend rods II4 threaded at each of its ends.

For vertical gas-flow, each of the sides 96 and 98 has secured thereto at its bottom an angle II8 upon which the edges of the ground plates 40 may rest and thereby be supported. In assembling the unit the required number of ground plates 40 and insulated plates 42 with spacers between them are disposed in the casing with the ground plates resting on the angles H6. The holes for the rods II4 are located in the sides I00 and I06 so that upper rods are just above the top of the ground plates 40, and the lower rods are just below the bottom of the plates. With the plate-electrode assembly in the casing, the side I06 is clamped toward the side I00 by means of nuts I I0 secured to each of the threaded ends of the rods I I 4. However, it is preferred that the tightening be performed by turning the nuts at the'side I 06. Screws I20 pass through slots II 2 and fit into suitable threaded holes in the casing sides and 98, so that slots II2 move relatively to the shanks of these screws while the precipitator- plates 40 and 42 are being. clamped together with the spacers I8 therebetween. When the clamping reaches the desired degree, the screws I20 are suitably tightened against the flanges to fasten the side I06 to the sides 96 and 08.

In a completely assembled casing the ground plates 40 are supported, as aforesaid, primarily on the angles IIO, while each of the plates 42 intermediate a pair of ground plates 40 is supported through the medium of the spacers between them. Consequently, the spacers perform the additional function of supporting each insulated plate 42 from a pair of adjacent ground plates 40. If desired, each of the sides I00 and I00 may also be utilized as ground electrodes equivalent to a plate 40, and this embodiment is indicated in Fig. 7 by the provision of holes I24 distributed over the sides and aligned with of approximately 14" and a height of 10", approximately, and a length of approximately 20" in the direction of air-flow. Within such a housing I30 is disposed the three zones A", B" and C" somewhat equivalent to the zones A, B and C of the embodiment shown in Fig. 1. In this embodiment, the precipitator-plates are all arranged in substantially vertical planes and the closely spaced plate-electrodes of the zone C" are clamped between spacers as in the first embodiment. not mounted in a casing such as the casing 94 of the prior embodiment but instead are clamped together by means of similar clamp rods between the two end plates which are somewhat heavier stock for rigidity. However, a casing havinga design similar to that of casing 94 but with sides in the form of open framework can be used. Consequently the assembled closely-spaced plateelectrode assembly is open at its sides and its top and bottom, and this unit is inserted into the housing I30 with a pair of suitable small vertical baflles I3I extending the height of the housing arranged between the end plates and the sides of the housing to obstruct any air-flow thereat. Above the precipitator-plates of the zones B" and C", the housing I30 is provided with an all compartment I32 comprising the top I34 of the housing and a perforated bottom wall I36 which is provided with a multitude of holes I38 through which oil squirts for washing the accumulated dirt from the precipitator-plates. In the embodiment shown, this oil compartment also extends over the ionizing zone A". The housing I30 comprises a gas-duct means for an airstream' therethrough.

The bottom of the housing I30 has a slightly downward slope in order to cause the washing oil to drain to an outlet pipe I40, the bottom having an up-tumer lip or rib I42 to provide a shallow pan between the bottom of the housing and its two sides. An inlet pipe I44 is provided for the oil compartment I32 through which oil is supplied thereto.

Three stage or zone air-cleaning precipitators such as described herein are particularly useful for cleaning air. In general, dust particles in air average, as measured with available equipment, about .45 micron in size, which average probably would be at an even lower figure if it were possible to measure the most minute dust However, the plate-electrodes are 7 region 'for breakdown. This can be better understood effects of flat electrodes. It that with spacings below ti the breakdown particles. However, in some locatities or on certain days, the number of larger sized particles may be quite considerable, and even fairly clean air may contain pieces of lint or-small pieces on a railway vehicle, the proportion of large cinders and grit in the air is large, so that the provision of a zone such as B or 2B" is highly desirable for an emcient small-size air-cleaning precipitator which will not require attention for a relatively long period of time.

the power supply means,

The close spacing of the plates of the last cleaning zone makes it desirable to wash the accumulated dirt from the preclpitator-plates occasionally, and rather than include an oil reservoir and an oil pumping means in the precipitator unit, it is preferable to provide external hose or pipe connections which can be connected to the respective pipes H0 and I, these pipes having detachable couplings M6 for such a purpose. A

I consider the use of normal close spacings for precipitator-plates in the order of ti or V or less, and preferably in the neighborhood of /8" plus or minus 36 a highly desirable advantage for electrical precipitators because of the relation of breakdown gradient and operating gradient in the close spacing region.

The close spacing in the order of A of an inch or less between precipitator-plates decreases the objectionable efiects of variations in the electrode-spacing because spacings of that order cause the precipitator to operate in the which requires very high voltage gradients with reference to Fig. 14 which is a curve showing breakdown gradient in kilovolts per inch as ordinates as compared to the spacing in fractions of an inch between two large spherical electrodes, spheres being used to avoid the edge may be observed gradient increases very rapidly for decreased spacings, introducing a greater margin of safety for irregularities in spacing along spots where the plates may not be exactly flat, but-even considerably deflected. A further advantage of using spacing of less than $4 resides in the fact that higher operating gradients can be used because of the greatly increased gradients required for breakdown at the points or spots on the plates where the deflections, or variations in spacings or the equivalent, occur. Consequently, although the proportionate increase in the voltage gradient between closely spaced plates having a fixed voltage applied across them is greater than with the more widely spaced plates, the operating safety factor is not necessarily decreased with spacings in the region which embraces the upper part of the bend of the curve of Fig. 14.

With close spacings irregularities or deflections in the flatness of the p'recipitator-plates can be tolerated, but excessive deflections at spots must be avoided because of undue air-flow resistance and lack of room for collecting reasonable amounts of dust without bridging, or almost bridging, the space between the electrodes which would produce excessive flashovers or spitting.

With closely spaced electrodes, the number of anchoring points need not be large because some variations in the spacing between the adjacent closely-spaced precipitator-plates can be tolerated, as previously pointed out. Consequently, it is desirable to incorporate means for preventing excessive deflections of the closely-spaced plates. The spacers i8-of my invention also perform this function for they anchor the precipitatorplates at their points of contact therewith, thereby fixing the spacing between precipitatorplates at a plurality of points distributed over their area, and limiting the extent of the deflections'between the anchoring points.

The use of spacers has the further important advantage of permitting the use of thinner plates, which may be either rigid or flexible, as distinguished from rigid plates heretofore solely used. In other words, the requirement for flatness and rigidity can be relaxed since the distributed anchoring points keep the precipitatorplates properly spaced regardless of the shape of the plates. In precipitator-units built in accordance with the present invention sheet metal of 13 mils thickness has been used for making the plate-electrodes as. compared to sheets of 30 milsor more, considered desirable in the precipitator units built in accordance with the aforesaid Pegg patent andthe Pound, et a1. Patent No. 2,212,885. Such thin sheets, utilizable with the instant invention, need have very little stiflfness because the numerous spacers keep them spaced without permitting any appreciable displacement; and an embodiment of my invention has been made in which each of the precipitator-plates, such as Ml and 42, was made of metal sheets cut to electrode size, which did not have suflicient stifiness to prevent a distinct bending under its own weight when supported horizontally at one end. Clamped with spacers therebetween, however, the thin electrodes maintained an ample degree of form and could not be objectionably deformed even by applied forces in the order of those to which precipitator-plates might be subjected.

The above-described factors permit me to decrease the size of practical precipltator-units considerably. The first precipitating zone removes the larger dust particles, leaving the collection of the finger dust particles to the final precipitatinga zone whose closely spaced plates will not be frequently spitting or flashing over because the larger particles, which might cause such spitting, have been removed, and accumulated dirt is frequently washed off.

The physical characteristics of a unit for cleaning air, such as shown in Figs. 12 and i3, illustrate the advantages of my; invention. In this unit the ionizing zone and first stage of precipitation extended about 11'' in the direction of air-flow,- with the high voltage plates having a length of 6%f, and spaced 1%" from the ground plates. The final precipitating stage comprised ground plates 13" by '7" in the airflow direction, spaced .14" from insulated plates 12 /2" by 6 A direct-current voltage of about 13,000 volts was applied between the ionizing electrodes, and consequently between the first stage preclpitator-electrodes, producing a non-ionized electrostatic field with a voltage,

gradient of about 7500 voltsper inch between these precipitator-electrodes; and a direct current voltage oi about 3300 volts produced a voltage gradient of about 24,000 per inch between the closely-spaced plate-electrodes. Air flowing through this unit at a velocity of about 900 feet per minute was cleaned with an efliciency of 85 to 87%, as measured by the Bureau of Standards Blackness test. For a 95% efilciency, the velocity had to 'be lowered to a discharge velocity of about 690 feet per minute, but even this velocity is considerably above permissible velocities, for the same efilciency, through prior commercial precipitator-units of the same general type for handling the same total volume of air, and which are of much larger size.

I findit desirable to utilize slightly. higher ionizing voltages for cleaning gases flowing at high velocities and slightly higher field gradients in the closely spaced plate-electrodes, the latter gradients being obtained, however, with lower overall voltages.

A further improved form of my invention is described and claimed in a copending application of Edward H. R. Pegg, Serial No. 442,052, filed May 7, v1942.

While I have described my invention in preferredforms, it is evident that it is subject to many modifications, and the use of a plurality of spacers at a plurality of points distributed over the surface of the precipitator-plates can be applied to plates which are generally fiat or bent, and that the use of distributed spacers results in numerous advantages.

v I claim as my invention:

1. Electrostatic precipitating-apparatus for removing foreign particles from a gas-stream, comprising the combination, with duct-means for maintaining said gas-stream, of ionizing-means for ionizing, without entirely precipitating, foreign particles in said gas-stream, and precipitating-means for precipitating charged particles from said gas-stream, said precipitating-means comprising a plurality of closely spaced, thin, flexible, precipitator-plates having a plurality of insulating spacer-means distributed at a plurality of points across their surfaces, means for holding said precipitator-plates in assembled relation, with their spacers between them, and means for maintaining an electrostatic potential-difference between said precipitator-plates.

2. The invention as defined in claim 1, characterized by the spacings between said precipitator-plates being of'the order of three-sixteenths of an inch, or less.

3. The invention as defined in claim 1, characterized by the spacings between said precipitator-plates being sufficiently small so that the operation is in a region where the breakdowngradient between the plates increases materially at points at which the plate-spacings may be slightly less than the average spacing.

4. The invention as defined in claim 1, characterized by the plates having precipitate-holding surface-means having materially greater ability, than smooth, dry surfaces, for resisting the blowing ofi of precipitated particles.

5. The invention as defined in claim 1, in combination with means for treating the plate-surfaces with a liquid.

0. The invention as defined in claim '1, characterized by the edges of the spacer-means being shaped so as to provide a Dlate-to-plate leakagepath which is materially longer than the plateto-plate spacing. v

7. The invention as defined in claim 1, characterized by the spacer-means and the precipitator-plates being so disposed and arranged as to provide interlocking protuberances and corresponding holes into which said protuberances project, for positioning the several parts which constitute the precipitating-means.

8. Electrostatic precipitating-apparatus for removing foreign particlesfrom a gas-stream, comprising the combination, with duct-means for maintaining said gas-stream, of ionizing-means for ionizing, without entirely precipitating, foreign particles in said gas-stream, and precipitating-means for precipitating changed particles from said gas-stream, said precipitating-means comprising a plurality of precipitatcr-plates,

spacer-means therebetween, means for holding said precipitator-plates in assembled relation,

with their spacers between them, and means for maintaining an electrostatic potential-difference between said preclpitator-plates, the plates of one polarity having edges extending out further than the plates of another polarity, in combination with support-means for engaging said extending edges.

9. Electrostatic precipitating-apparatus for removing foreign particles from a g as-stream, comprising the combination, with duct-means for maintaining said gas-stream, of ionizing-means for ionizing, without entirely precipitating, foreign particles in said gas-stream, and precipitating-means for precipitating charged particles from said gas-stream, said precipitating-means comprising a plurality of precipitator-plates,

spacer-means therebetween, means for holding said precipitator-plates in assembled relation,

with their spacers between them, and means for maintaining an electrostatic potential-difference between said precipitator-plates, the edges of the spacer-means being shaped so as to provide a plate-to-plate leakage-path which is materially longer than the'plate-to-plate spacing,

10. Electrostatic precipitating-apparatus for removing foreign particles from a gas-stream, comprising the combination, with duct-means for maintaining said gas-stream, of ionizing-means for ionizing, without entirely precipitating, foreign particles in said gas-stream, and precipitating-means for precipitating charged particles from said gas-stream, said precipitating-means comprising a plurality of precipitator-plates, spacer-means therebetween, means for holding said precipitator-plates in assembled relation, with their spacers between them, and means for maintaining an electrostatic potential-difierence between said precipitator-plates, the spacermeans and the precipitator-plates being so disposed and arranged as to provide interlocking protuberances and corresponding holes into which said protuberances project, for positioning the several parts which constitute the precipitating-means.

l1. Electrostatic precipitating-apparatus for removing foreign particles from a gas-stream, comprising th combination, with duct-means for maintaining said gas-stream, of ionizing-means .spacer-means therebetween, means for holding said precipitator-plates in assembled relation,

with their spacers between them, and means tor maintaining an electrostatic potential-diflerence between said precipitator-plates, and spraymeans built into one wall or the gas-stream duct alongside of an edge of the precipitator-plate structure, said spray-means having perforations opposite to the spaces between the precipitatorplates, and including means for causing a liquid to be discharged through said perforations.

12. A precipitating means for an electrical gaspurifying precipitator for cleaning dust from a flowing gas, comprising a plurality of precipitator-plates substantially paralleling the gas-flow, said plates being arranged in two relatively insulated series with alternate plates in a series, insulating spacer means including spacers for spacing said plates, supporting means for one of said series of plates, the last said series of plates and said spacer means having interlocking means for positioning saidspacers, the other series of plates and said spacer means having interlocking means for supporting the said other series of plates by said spacer means.

'13. A gas-purifying electrical precipitator apparatusror cleaning dust-particles from a flowing alias, such as air, comprising a precipitating means for precipitating charged dust-particles, said precipitating means comprising a plurality of precipitator-plates paralleling the gas-flow and arranged in groups with alternate ones of said plates 10 in a group, said plates having apertures at a plurality of points distributed ,over their areas, spacer means for insulating th respective groups of plates, said spacer means comprising separate insulating spacer devices between adjacent plates,

15 having interlocking provisions cooperating with 20 plates.

GAYLORD W. PENNEY.

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