US2448046A - Precipitator - Google Patents

Description

Aug. 31, 194s. G. w. PENNEY Em. 2,448,046

PRECIPITATOR Filed July 6, 1945 2 Sheets-Sheet 1 G. w. PENNEY ETAL l2,448,046

rnEcIPITA'roR Aug. 31, 194s.

.2 Sheets-Sheet 2 Filed July 6, 1945 Uv? J0 Patented Aug. 31,V y1948 PRECIPITATOR Gaylord W. Penney, Wilkinsburg, and George W. Itlewitt,Pittsburgh,` Pa., assignors to Westinghouse Electric Corporation, E ast Pittsburgh, Pa., `a corporationof Pennsylvania yapplication Julys, 1945, seriaiNt. 603,503

(o1. iss-J1) 20 Claims.

This invention relates to electrostatic dustprecipitators for the efcient cleaning of a gas, particularly air owing at relatively high velocities. This invention also relates to a pumping System useful for keeping the dust-collecting electrodes of Ielectrostatic dusteprecipitators clean. n

It is among the objects of our invention to provide an electrostatic dust-precipitator vof high capacity for its size so that it may be'effectively used in places Where the space available for receiving the dust-precipitator is limited-or accessible With difficulty.

It is a furtherV object of ourinvention to provide an electrostatic dust-precipitator system of a type having separate dust-charging means and dust-precipitating means, each comprising "a plurality o f electrodes, and means for periodically cleaning electrodes With clean liquidleach time.

An additional object of ourinvention is to provide an electrostatic dust-precipitator of the aforesaid type, having novel self-contained cleaning means for removing dirt collected on its dustcollecting electrodes, which means canbeo'perated either While gasis flowing through the dustprecipitator for cleaning, or While the gasiiow is stopped and the electrical energization of the dust-precipitator interrupted.

The invention described herein isbased upon, and in a sense constitutes a `continuation-iri-igiart and improvement over, the invention disclosed and claimed in our copending application Seriall No. 544,581, led July 12, 1944. In the latter application, We disclose a system comprising an electrical dust-precipitator having dust-collecting electrodes which constitute part of a predetermined loop-circuit in which a liquid is cir-v culated for removing precipitated dust from/the dust-collecting electrodes, and leaving aI fresh layer of cleaner liquidon their surfaces for improving the retention of` subsequently precipitated dust. An important feature resides in pro-i viding a combined structure Whichpermitsthe use of the same liquid over and over for cleaning the dust-collecting electrodes, the liquid being storedin a reservoir or tank from Whicha suitable quantity is Withdrawnfor use in the loop'- circuit and returned after; use. During. useA for cleaning the dust-collecting electrodes, the 'liquid circulates aroundand around in the loop-circuit The liquid itself is cleaned in the intervals between the periods in which it circulates in the loop-circuit, the cleaning of the liquid being done by electrostatic means because We have found that such meansquickly and eifectively ycleansv a liquid containing dirt such as is electrostatically precipitated `from air. The liquid-cleaning electrostatic' means is lassociated with the tank in such manner that aisludg'e is formed which falls intoasepar'ate portion of the tank. A further feature of theinvention described in our cepending application resideslin providing an arrangement for preventing sludge from mixing back into the cleaned liquid when the latter is Withdrawn for cleaning the dust-collecting electrodes or when dirtyrliquid is returned to the tank after USB;

An important object of the present invention isto provide a system of the aforesaid type in which aliquid withdrawn from the tank can be circulated in aloop-circuit that does not include any part of the tank. However, an open pipe connection is provided between the tank and loop-circuit through which liquid for circulation can at any time be Withdrawnfrom the tank by the starting of a pump, and returned to the tank when the pump .is stopped. By segregating the loop-circuit entirely from the tank, the liquid that travels around the loop-circuit is much less likely todsturb-sludge in the tank or other liquid in the tank undergoing4 cleaning at the same time or havingcr'Jnce'ntratedv dirt in it. This'means that the speed and volume at which-the liquid circulates in the loop-circuit can be materially increased, other conditions being the same.

A further object of our invention is to progressively clean an assemblyl of dust-collecting electrodesina special manner. Only an increment of the assembly is cleaned at a time, the volume of the cleaning liquid being suicient to substantially fillothis increment with liquid flowing suiciently strongly tovforcefully flush collected dirtifrom the surfaces of the dust-collecting elec- `trodesbeing cleaned. The cleaning liquid may be, of course, any suitable substance, of which a number'arek known.. If desired, the liquid may berone for coating the surfaces of the dust-collecting electrodes and one which flushes off easily.

Many objects, features,combinations, andv in- 3 novations of our invention in addition to the foregoing and those described in our aforesaid copending application, will be discernible or obtainable from the following description and accompanying drawings, in which:

Figure 1 is a schematic vertical View, partly in section, illustrating the principal features of our invention;

Fig. 2 is a schematic plan view of an assembly of a plurality of dust-collecting electrodes, provided with a means movable across the top of the assembly, in a direction transverse to the gas flow, for cleaning them;

Fig. 3 is a schematic elevational view of the apparatus of Fig. 2, looking upstream;

Fig. 4 is a broadside sectional view for illustrating an assembly of a plurality of relatively alternately insulated and uninsulated plateelectrodes;

Fig. 5 is a perspective view of a group of spaced dust-collecting plate-electrodes having plate-cleaning means associated therewith, the latter being shown in greater detail than is shown in Figs. 2 and 3; and

Fig. 6Ais a simplified electrical wiring diagram of an operating and controlling apparatus embodied in our invention.

Referring more particularly to Fig. 1, a gas duct 2 is shown in which a gas flow is established in the direction of the arrows A by a blower means 4 which includes an electric motor 6. A gas-cleaning electrostatic dust-precipitator is arranged in the gas duct 2 and comprises an up-stream ionizing or dust-charging means 8 in which gas-borne dust particles receive an electrical charge, and a down-stream dust-precipitating means I0 in which charged dust particles are removed from the 'gas stream.

The ionizing means 8 includes a plurality of relatively insulated electrodes spaced laterally across the gas duct, and comprising insulated relatively ne ionizing wires I2 and relatively large round-rod uninsulated electrodes I4. The electrodes I4 are periodically rotated by an electric motor I6. Jets I8 supply a cleaning liquid to each electrode I4 when it is rotated. Dustcharging apparatus of this kind is described and claimed in our copending application, Serial No. 784,330, filed November 6, 1947.

The dust-precipitating means Ill comprises an assembly of a plurality of upstanding relatively insulated and uninsulated plates 28 and 22, respectively, held spaced by a plurality of individual small insulators 24, as shown in Penney Patent 2,347,709, dated May 2, 1944. An insulated plate-electrode 20 is between each pair of consecutive uninsulated plate-electrodes 22, with its edges within the rectangular contour of the uninsulated plate-electrodes. The assembly includes a plurality of spaced elongated clamping rods 26 passing through the plates, oversized holes being provided in the insulated plates for added insulation protection. However, any suitable plate-assembly with an open top into which cleaning liquid can be directed, can be used. The rectangular plate-assembly extends across the gas-stream path in the gas duct '2 and is supported with its upstanding edges tilted with the top further downstream than the bottom.

Insulated conductors 38 and 32 convey high potential to the ionizing wires I2 and to the insulated plate-electrodes 20, respectively.

A plate-cleaning means, indicated in its entirety by the reference numeral 34, is arranged to travel across the top and an upstanding downstream side of the plate-assembly of the dustprecipitating means, being guided and supported on upper and lower transverse rods 36. As shown more clearly in Fig. 5, the plate-cleaning means 34 comprises a nozzle-device 38 having a chamber 40' with a bottom wall 42. The chamber receives liquid through an inlet pipe 44, and the liquid flows out of the chamber through a rectangular discharge-mouth 46 having a plurality of spaced partitions 48 for directing the liquid flowing out of the chamber. The discharge-mouth 46 is about as long as the width of the plate assembly, and its open width spans one, or at most a few, of the spaces between the plate electrodes 20 and '22; the number spanned being a very minor part of the total number of such spaces provided transversely across the gas duct 2 by the dust-precipitating means Ill. The bottom wall 42 spans several more spaces than does the discharge-mouth. The plate-cleaning means 34 also comprises an upright baffle plate 50 which is about the height of the plate-assembly and extends laterally beyond both sides of the bottom wall 42. The insulated plates 2U are suiiciently inside the edges of the plates 22 to provide adequate air-insulation between the high voltage plates 20 and the grounded plate-cleaning means as the last moves past them, as close to the edges of the plates 22 as mechanical considerations permit.

The plate-cleaning means 34 is moved across the dust-precipitating means by any suitable mechanism. That shown comprises an apertured block 52, secured to the plate-cleaning means, preferably to the baffle plate 50. The apertured block 52 has an upstanding elongated slot which receives a pin 54 extending from an endless sprocket chain 56 that engages a pair of sprocket wheels 58 and 60 at opposite sides of the gas duct 2. The sprocket wheel 60 is driven by an electric motor 62 through gearing 64. When the sprocket chain 56 is moving, the pin 54 forces the plate-cleaning means 34 in one direction when the pin 'is in the upper horizontal stretch or portion of the sprocket chain, and in the reverse direction when it is in the lower stretch.

The apertured block 5'2 carries a depending lug 66 which operates limit switches 68 and 'I0 at the ends of the path or stroke in which the plate-cleaning means 34 travels; these limit switches being normally biased to circuit closing position, and operated to circuit opening position when engaged by the lug 66.

It is intended that the amount of cleaning liquid discharged from the nozzle-device be sufficient to fill several of the spaces between the plate-electrodes 2D and 22, and that the liquid flow toward the upstream side of the plate-assembly as well as downwardly. To this end a lower closure plate 12 (Fig. 1) is provided which extends across the gas duct 2 and vcooperates with the baffle plate 50 and the nozzle-device 38 to substantially enclose the associated spaces on three sides, thereby forcing liquid discharged at a suitable rate to ll these spaces and to flow forwardly, as indicated generally by the arrows B. Liquid-receiving means or troughs are provided across the gas duct to receive the liquid passing from the dust-precipitating means. A trough 'I4 below the front or upstream edge of the dust-collecting plate-electrodes receives most of the liquid. A small portion of the liquid is permitted to Il'ow intoa back trough 16, the

amount being controlled by the clearance between the bottom edge of. the baffle .platev 50 and the proximate horizontal edge of the transverse closure plate 12. The` troughs 14 and 16 slope downwardly to drain pipes 18 and 80, respectively, which meetat a; junction 82 where the different portions` of the liquid recombine after having cleaned the plate electrodes.

Liquidforf cleaning the plate-electrodes is held in a reservoir or tank 90 from which liquid is withdrawn when the plate-cleaning means is in operationandto which liquidv returns when the plate-cleaning means is not in operation. Inasmuch asl the liquid becomes contaminated with dirt after passing through the plate-assembly, the tank 9 gis providedwith. anl open. electrostatic liquid cleaner 8 2, The cleaner 92 comprises a plurality of alternately relatively insulated and uninsulated platesil which extend below the level of the liquid in the tank.. When a unidirectional electrostatic iield is established between the plates 93, dirt inthe liquid concentrates in the liquid at and between the plates, so as to form a sludge that drops into a sludge-receiving portion 94 of the tank. A unidirectional electrostatic field causes quiet liquid in the tank to substantially imperceptibly drift to, into and from the spaces between the plates 93 of the cleaner 92, and soon cleaned liquid is found in a portion $6 of the tank. Additional details of a tank including a cleaner along the lines herein described may be found in our aforesaid application, Serial No. 544,581.

For withdrawing liquid from the tank and usingl the liquid. for cleaning dust-collecting electrodes, a pumping system is provided which comprises a loop or loop-circuit external to the tank 9B and a piping means interconnecting a lower portion of the loop-circuit with a lower portion ofA the tank ai), preferably its cleaned oil portion Qt. the troughs 14 and 16 and pipes 18 and Sil in parallel, the junction 82, a pipe lili] from the junction 8 2 to the inlet end of a pump 98, the pump 98, a loose flexible hosing |02 from the discharge end of the pump to the inlet pipe ed of the nozzle-device 38, nozzle-device 38, and the dust-collecting plate-electrodes `of the dustprecipitating means `lil. While the loop-circuit can be considered to include all of the dust,-

collecting plate-electrodes, it should be noted-` that cleaning liquid ows only through avery small part of the spaces provided'by themat any single instant. There is enough playl in the hosing |02 to-follow the movement of the nozzledevice across the top of the vdust-collecting plateelectrodes of the dust-precipitating means i0.

A- small branch |Il4 takes some liquid from the described Vloop-circuit and delivers it tothe jets I8-, returnliquidowing into the trough 14.

An open pipe Iti` is provided for the free exchange of liquid between the loop-circuit and the tank 90 this pipe |96 having an open end in the lower part of the cleaned oil portion 96 of the tankl and another end at the junction 82 at the bottom of the loop-circuit. The loop-path is for themost part above the level of the liquid in the tank 90 which should -beof sufficient size to receive all the liquid of the system except for tha-small portion that might be contained inthe various pipes below the liquid level in the tank. The pump 88 has its intake below the normal level of liquid in the tank, which is roughlyv indicated at C, by. normal level meaning the liquid level when the pump is not operating.

Platecleaning may be carried out for consid- The loop or loop-circuit consists off ,the circuit |55.

erably' different lengths, of .timel For example,

.acrossthe plate-assembly and back, as often. as

desired. Stillanothermethod-of operation would be to-permit the nozzle-device tomove indeiinitely .back and forth across Athe gasfducubeingstopped only long enough to permit liquid-to be cleaned.

.If clean, liquid is continuously Supplied to the nozzle-device,` it can be permitted tomove continuously;

Fig. .6 shows a flexible control system which permits various sequences of plate-cleaningoperations, When normally deenergized relay |08 isenergized,y the front contacts LID-and |12 close, these contactsbeing, respectively, in circuitsI |.|4 and HB for `themotors 62 and i6, respectively. The motorzdrives the plate-cleaning means34, and, in the preferred embodiment, also operates thejpump 98, through any suitablegearing, if necessary. The motor lrotates-the,uninsulated electrodes |,4 ,of` the ionizingmeans When-,the contacts! l0 and I i2 are inopen or back position, which is the case when the relay |il8is `deenergizecLthe motors |52 and |6vdo not operate. It is also possible to prevent operation oi the motor E6 when the contacts l2 are closed by opening a manually-operable normally-closedswitch I |-8 in Anormally deenergized relay |223 `has back contacts closing energizing circuits |22 and |24, respectively, for the blower motor and a, high voltage direct-current supply, such as power pack lZt. VThe former creates a gas ow in the gas duct 2, and the latter supplies various directcurrent high voltages to thev insulated electrodes of the system.`

With a control system in the conditionshown in Fig. 6, bothirelays |8 and E20 are deenergized, and theequipment of Fig. 1 wouldbe operating to clean the gas stream in the gas duct 2v and the liquid in the'tank 90; The electrodes |4 the pump 93, and the plate-cleaning means 34 would be stationary.

A If it is desired tomanually operate the platecleaning means with the gas-cleaning means stopped, ya normally-open manually-operable switch |28 may be closed, thereby causing both relays ||8 andll|20 to, be energized. Uponvreopening the switch |28, after any desired time, the gas-flowing gas-'cleaning operation is restored. As an addedsafety measure, a normally closed switch |30 may bel provided interlocked with the switch |28, so as to be closed whenthe latter is open, and vice versa.

If itis desired to automatically periodically operate the plate-cleaning means with gas flow shut down and the power pack |26 deenergized, the switch |28 should remain open and the switch |30 closed so that al timer |32 will be energized. The timer may operatefor closing a timer switch |34 onceevery few hours, say, for example, every ten or twenty hours. It remains closed until, lug 6,6 leaves a limit switch and permits the latter to close.

`The relaysl |08and |20will be energized while the timer switch |34 is closed, thereby deenergizing` the motor 6 and the power pack` |26, and energizing ,the motors |6 and- 62. Assume that the nozzle-device was at the extremev right where it operated to open limit switch 1B. Rotation of the motor 62 movesthe plate-cleaningmeans 34 and its nozzle-device 38 toward the left, so that the limit. switch 'lll closes, establishing a new energizing, or' lilding, circuit |3'6` for the relays |08 and |20, the last circuit including the limit switches 68 and '|0 in series. Consequently, a1- though the timer switch |34 reopens, the relays |08 and |20 will remain energized through the circuit |36 until the plate-cleaning means 34 reaches .its extreme left-hand position, at which its lug 66 operates to open the limit switch 68, interrupting the holding circuit |36 to the relays |08 and |20. Deenergization of these relays re-establishes gas ow and stops electrode cleaning. When the timer switch |34 closes again, the re- .lays |08 and |20 are reenergized, and the motor -.62 starts to move the plate-cleaning means to the right, permitting the limit switch 68 to close and thus re-establish the secondary holding circuit |36 for the relays until the plate-cleaning means has moved to its right-hand position where it again opens the limit switch 10. By closing a normally-open manually-operable switch |40, the plate-cleaning means will make one complete back and forth traverse of the dust-collecting electrodes every time the timer switch 34 operates.

If the cleaning of the dust-collecting electrodes is to be accomplished without interrupting the cleaning of the flowing gas, normally-closed manually-operable switch |42 may be opened for preventing energization of the relay |20 and consequent interruption of the circuits |22 and |24 for the blower motor 6 and the power pack |26, respectively. This is the manner in which we prefer to operate the apparatus.

We consider the operation of the pumping system in connection with electrostatic dust-precipitators an important feature. Referring to Fig. 1, when the pump 98 first starts to operate, cleaned liquid in the tank 90 is drawn into the pipe |06 and passes through this pipe into the lower part of the previously described loop-circuit; more specifically, into the pipe and to the intake of the pump 98. The pump forces the liquid through the hosing |02 into the nozzle-device 38 where the liquid is discharged into the plateassembly but only into the spaces of the dust-collecting electrodes with which the dischargemouth 46 of the nozzle-device is associated. Three sides of these spaces are blocked olf by the bottom wall 4'2 of the nozzle-device, the baffle plate 50, and the closure plate '|2. .The capacity of the pump is sufficient to force the liquid through the few spaces under the discharge-mouth with considerable force, and the barrier means around the three sides of the spaces causes them to be filled with this forcibly flowing liquid. By arranging the baffle plate 50 along the downstream side, the cleansing liquid flows forwardly, except for the small amount that is permitted to pass into the trough 16. After washing the surfaces of the dust-collecting plates, the liquid ows into the troughs 14 and 16 and through drain pipes 'I6 and 80 to the junction 32 from where it flows again into the pipe |00 leading to the intake of the pump 98. The pump will draw liquid from the tank until the amount of liquid flowing back through the drain pipes is substantially equal to the pumps intake capacity. After this, the liquid recirculates around the loop-circuit over and over without visibly disturbing the liquid in the tank. When the pump 98 stops, liquid drains out of the upper portion of the loop-circuit, flowing back into the tank through the pipe |06` and raising the level of the liquid therein.

The pipe |06 can be restricted sufficiently, or an artificial restriction provided, so that liquid withdrawn or returned to the tank passes through it at a rate which does not significantly disturb the quiescence of the sludge in the tank. Preferably, however, the rate during withdrawal should be sufficiently adequate to prevent objectionable lowering of the liquid head in the pipes 'I8 and 80. The head of the liquid in the tank should be sufficiently above the lowest allowable level in the pipes I8 and 80 to supply the friction head or drop in the pipe |06 from the tank to the junction 82. This condition also prevents the pump from sucking air. When the pump is operating, the head of liquid in the pipes 'I8 and 80 will rise above the level in the tank to an extent depending on the friction drop in these pipes. The pipes 'I8 and 80 should, therefore, be comparatively large in order to prevent the liquid from overflowing the troughs. Preferably, the friction drop should be limited, but the bottom part of the loop-circuit need not hold much liquid when the liquid is not being recirculated.

Several distinct advantages are obtained by limiting the number of dust-collecting electrode surfaces to be cleaned at the same time and by filling the spaces therebetween with forcibly flowing liquid that flows forwardly or upstream. One advantage is that most of the dirt electrostatically removed from the gas stream usually precipitates in the front part of the dust-precipitating means, so that the forwardly moving liquid does not have to carry this heavy dirt deposit through the entire width of the plate-assembly. A second advantage arises from the fact that lint is usually caught on the front edges of the dust-collecting electrodes and will be washed outwardly, minimizing any chances of these long pieces of dust-particles bridging oppositely charged dust-collecting electrodes.

In a practical apparatus, to which our invention is, however, not limited, satisfactory operation was obtained with a nozzle-device having a discharge-mouth extending for substantially the full width of the insulated plate electrodes, but not quite to the upstream edge, and having an open width slightly less than the distance between two consecutive uninsulated electrodes 22. These uninsulated electrodes were about 28 inches high and about 61/2 inches wide. The spacing between facing relatively insulated electrodes was .145 inch, with the total number of spaces being well over a hundred. The plate-cleaning means travelled across the plate-assembly at a rate of nearly one-half inch per minute, while cleaning liquid flowed out of the nozzle-device at a rate of close to nine gallons per minute and at a velocity of about 200 feet per minute. Near the top of the plate-assembly, the liquid has an average velocity of about 50 feet per minute downward. Further down in the plate-assembly, the downward component of velocity decreases and the forward component increases, but not to the same degree because of liquid flowing out of the plate-assembly. By slowing down the rate at which the plate-cleaning means travels, the quantity of liquid flowing across the surfaces of the dustcollecting electrodes may be further increased.

Where it is desired to permit gas ow while the dust-collecting electrodes are being cleaned, so as not to interrupt the clean air-supply, the bottom wall 42 of the nozzle-device 38 and the baffle plate 50 should be wider than the dischargemouth 46 so as to allow liquid to drain from the spaces which the discharge-mouth has just passed or uncovered, while gas flow therethrough is barred, the gas being diverted into other spaces. The slow travel of the plate-cleaning means allows for a suitable -time of drainage, but ob-4 viously the width of the' bottom wall 42 and the baie plate 5U may fbe made to correspond to the rate of travel of the plate-cleaning means.

Because the edges of the baille plate and nozzledevice extend laterally beyond the dischargemouth, the gas duct can be 'provided with closed sections at each lateral end ofthe dust-precipitating means and suitable baiiles such as the bale M4 in order to divert the gas flow from spaces not provided with dust-collecting electrodes which can'be washed.

While we'have described ourinvention in a form at present preferred, other forms are Valso useful and possible. Our invention is subject to wide modification and many equivalent elements may be substituted therein, or otherwise used, based upon the teachings of our invention.

We claim as our invention:

1. A system of a type described, comprising 'an electrostatic dust-precipitator for cleaning a gas flow, comprising gas purifying means comprising a plurality of spaced dust-collecting electrodes; a loop-circuit including therein: a pump, said dust-collecting electrodes, a nozzle-device con-v nected to the discharge end of said pump'and movable across said dust-collecting electrodes, `a trough means extending below said dust-collecting electrodes, and a piping means between said trough means and the inlet of said pump; distinct container means outside of said loop-circuit or cleaning and holding cleaned liquid for circulation in said loop-circuit, said loop-circuit extending above said liquid-holding means; a piping lconnection between said container means and said loop-circuit; and operable for operating rsaid pump during spaced periods and for moving said nozzle-device progressively across said dust-collecting electrodes; said piping connection beingopen during pump-operating periods and between such periods.

2. The invention of claim 1 characterized by said nozzle-device comprising a discharge-mouth spanning only a very minor part of the spaces between said plurality oi dust-collecting electrodes, and means for restricting' the outflow of liquid from said spaces as they are progressively spanned by said discharge-mouth, wherebyl the spanned spaces become lled with flowing liquid.

3. The invention of claim 1 characterized by said nozzle-device comprising a dischargemouth .spanning only a very minor part of the spaces between said plurality of dust-collecting electrodes, means for restricting the outflow of liquid from said spaces as they are progressively spanned by said discharge-mouth, whereby the spanned spaces become iilled with flowing liquid, and means for barring gas-flow through the spaces which are spanned and which have been just uncovered by said discharge-mouth, whereby to permit liquid'drainage from said uncovered spaces.

4. A system of a type described comprising a plurality of spaced upstanding dust-collecting plate-'electrodes through the spaces of `which a gas can flow, a nozzle-device having a dischargemouth spanning only a minor part of the spaces between said plurality of dust-collecting electrodes, moving means for slowly and progressively moving said nozzle-deviceacross the top edges of said plate-electrodes, abaie plate associated with said nozzle-device for barring iluid iiow'through'an upstanding side of the spaces spanned by said discharge-mouth, and permitting gas-now through the other spaces, means lOWplurality of spaced upstanding dust-collecting 10 for limiting iiuid flow through the bottom of said spaces, trough means for catching liquid flowing out fromsaid spaces, a pump having an inlet connected to said trough means and an out- ,let connected to said nozzle-device, a liquid reservoir extending below said dust-collecting electrodes, and a piping connection between said reservoir and the pump inlet.

5. A system Aoi atype described comprising a plate-electrodes through the spaces of which a gas'can ilow, a vnozzle-device having a dischargemouthspanning only a minor part of the spaces between said plurality of dust-collecting electrodes, moving means for slowly and progressively moving said nozzle-device across the top edges of said plate-electrodes, a baille plate associated with said nozzle-device for barring fluid iiow through an upstanding downstream side of the spaces spanned by said discharge-mouth and permitting gas-How through other spaces, means for limiting fluid flow through the bottom oi said spaces, a trough means for catching liquidflowing out from said spaces, a pump having an out- `let connected to said nozzle-device, said moving means being adapted to move said nozzle-device suniciently slowly for said pump to keep the spaces spanned by said discharge-mouth substantially full of Viiowing liquid, at least some of which ows with an upstream direction-component.

A6.\A system of a type described comprising `a plurality of spaced upstanding 'dust-collecting plate-electrodes through the spaces of which a `gas can ilow, a nozzle-device having a dischargemouth spanning only a minor part of the spaces between said plurality of dust-collecting electrodes, moving means for slowly and progressively moving said nozzle-device across the top edges of said plate-electrodes, a baffle plate associated with said nozzle-device for barring fluid flow through an upstanding downstream side of the spaces spanned by said `discharge-mouth and permitting "gas-flow through other spaces, said baille plate being wider than said dischargemouth for barring iiuid flow through spaces on both sides of saididischarge-mouth, means for limiting fluid flow through the bottom of said spaces, a trough meansior catching liquid iiowing out from said spaces, a pump having an outlet connected to said nozzle-device, said moving means being adapted to move said nozzle-device sufciently slowly for said pump to keep the spaces spanned by said discharge-mouth substantially full of flowing liquid, at least some of which flows with an upstream directioncomponent.

'7. The invention of claim 5 characterized by said pump having kan inlet connected to said trough meansVa liquid tank below said dustcollecti-ng electrodes, Vhaving electrostatic oilcleaning means and a sludge portion therebelow, andl a` connection between said pump inlet and a lower part of said tank.

8. The invention of claim 6 characterizedby said pump having an inlet connected to said troughtmeans, aliquid tank below said dustcollecting electrodes, having electrostatic oilc-leaning means anda sludge portion therebelow, and a connection between said pump inlet and a lower part of said tank.

9. A dust-precipitating means comprising a pluralityoi spaced upstanding alternately relatively insulated and uninsulated plate-electrodes, providing a comparatively large number of spaces for a gas-now, plate-cleaning means comprising a barrier-means and a nozzle-device for directing a liquid flow into a very minor number of the total number of said spaces, said barrier means comprising a baille plate along an upstanding side of said dust-precipitating means, and means operable for slowly and progressively moving said nozzle-device and said bailie plate across said plurality of dust-collecting electrodes, in proximity to the edges of the uninsulated plate-electrodes.

10. The invention of claim 9 characterized by said nozzle-device comprising a discharge-mouth, said baiiie plate spanning a greater number of said spaces than said discharge-mouth.

11. A dust-precipitating means comprising an assembly of spaced upstanding dust-collecting plate-electrodes through the spaces of which a gas can flow, said assembly having a tilted downstream side, with its top further downstream than its bottom, and plate-cleaning means comprising a nozzle-device movable along the top edge of said assembly, for directing a uid flow into a very minor part only of the spaces between said dust-collecting plate-electrodes, barrier means comprising a baiile plate along said tilted side for restricting fluid flow out of spaces receiving uid from said nozzle-device, land means for moving said nozzle-device across the top edge of said assembly.

12. The invention of claim 11 characterized by said nozzle-device comprising a discharge-mouth which is elongated in the direction of gas-flow and said nozzle device and said baille plate being wider than said discharge-mouth, and movable with it.

13. A dust-precipitator means comprising an assembly of spaced upstanding dust-collecting plate-electrodes providing spaces through which a gas can flow, said assembly having a tilted upstanding side, plate-cleaning means comprising means for discharging fluid into the spaces between said dust-collecting plate-electrodes, and barrier means comprising a movable barrier along said tilted side for restricting fluid ilow out of the spaces thereat.

14. The dust-precipitating means of claim 13, characterized further by said barrier means further comprising a second barrier along the bottom side of said assembly.

15. The system of claim 4, characterized further by said trough means comprising a trough at the downstream and upstream sides of said plate-electrodes.

16. The dust-precipitating means of claim 11 characterized further by said barrier means comprising a second barrier along the bottom side of said assembly.

17. A system of a type described, comprising an up-standing loop-circuit in which liquid can be recirculated, said loop-circuit comprising a pump in the bottom thereof an inlet pipe for said pump and a gas-treating means for receiving liquid from the outlet of said pump; means for intermittently operating said pump; a con-I tainer means for holding a denite body of liquid, said container means being outside of and separate from said loop-circuit; a connecting pipe extending from said inlet pipe to a lower part of said container means; said container means being on a level with a bottom portion of said loop-circuit and being large enough to hold all of the liquid draining from said loopcirouit through said connecting pipe into said container means when said pump is not operating; said pump when operating drawing liquid from said container means through said connecting pipe and recirculating it in said loop-circuit without mixing with liquid remaining in the container means; said container means having electrostatic liquid-cleaning means therein; and means for supplying a D. C. voltage to said electrostatic liquid-cleaning means.

18. A system of a type described comprising a lloop-circuit for recirculating liquid, said loopcircuit comprising: a liquid discharge device, electrostatic gas-treating means arranged to receive liquid from said liquid discharge device, a tro-ugh below the liquid discharging device, and a pump having an inlet connected to said trough; a container outside of said loop-circuit for liquid, said loop-circuit extending above said container, electrostatic liquid-cleaning means in said container, an open connection between a bottom part of said container and said pumpinlet, said connection and said pump-inlet being below the top of said trough, said container otherwise being separate from said loop-circuit, whereby liquid drawn from said container may be continuously recirculated in said loop-circuit without mixing with liquid remaining in the container.

19. A system of a type described comprising an up-standing loop-circuit in which liquid can be recirculated; said loop-circuit comprising a means ln which said liquid can be contaminated and a piping arrangement for the bottom of said loop-circuit, said piping arrangement comprising a pump and an inlet pipe for said pump; means for intermittently operating said pump; a container outside of and separate from said loop-circuit for holding the liquid to be recirculated in sai-d loop-circuit; an electrostatic liquidcleaning means in said container; a connecting pipe outside of said loop-circuit, extending from said inlet pipe to a lower part of said container; said container being at a level with said piping arrangement and being large enough to hold al1 of the liquid draining into it from said loopcircuit through said connecting pipe when said pump is not operating; said pump when operating drawing liquid from said container through said pipe and recirculating liquid in said loopcircuit; said piping arrangement, said connecting pipe and said container being so arranged that liquid is automatically drawn from said container into said loop-circuit upon initial operation of said pump and liquid is recirculated in said loop-circuit by said pump during operation of said pump without mixing with liquid remaining in the container, and is automatically returned from said loop-circuit through said connecting pipe to the container upon stopping of the pump so that the liquid can be cleaned by said electrostatic liquid-cleaning means.

20. A system of a type described comprising dust-collecting means, a pump, means for periodically operating said pump, means providing a loop-circuit, including said dust-collecting means and said pump, in which liquid can be continuously recirculated, a container outside of said loop-circuit for liquid to be recirculated in said loop-circuit, electrostatic, liquid-cleaning means in said container, means comprising an 'open pipe connection from a portion of said container for cleaned liquid to a bottom part of said loop-circuit, said loop-circuit comprising means arranged to automatically drain liquid from said container through said pipe connection into said loop-circuit upon initial operation of said pump.

13 and automatically return liquid from the loopcircuit through said pipe connection to the container by stopping of the pump, and to keep liquid recirculating in saidgloop-circuit from mixing with liquid remaining inthe container.

GAYLORD W. PENNEY. GEORGE W. HEWITT.

REFERENCES CITED Number UNITED STATES PATENTS Name Date Hagan Jan. 20, 1931 Whitney Oct. 20, 1931 Dantsizen Oct. 20, 1931 Strindberg Nov. 10, 1931 Goodloe June 28, 1932 Fedeler Jan. 31, 1933 Brelsford et ai. Mar. 27, 1934 Pegg Nov. 2, 1943

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