US2333551A

US2333551A - Electrical gas cleaning means

Info

Publication number: US2333551A
Application number: US431389A
Authority: US
Inventors: Edward H R Pegg
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1942-02-18
Filing date: 1942-02-18
Publication date: 1943-11-02
Anticipated expiration: 1960-11-02

Description

Nov. 2, 1943. E. H. R. PEGG 2,333,551

ELECTRICAL GAS CLEANING MEANS Filed Feb. 18, 1942 5 Sheets-Sheet 1 [dward/Z/Efia 1. BY jay //4@ 32mm MW/XZM M 4 ATTORNEY Nov. 2, 1943. E. H. R. PEGG 2, 3

ELECTRICAL GAS CLEANING MEANS Filed Feb. 18, 1942 5 SheetsSheet 2 INVENTOR [award/WP. P50;

Nov. 2, 1943. R PEGG 2,333,551

ELECTRICAL GAS CLEANING MEANS Filed Feb. l8, 1942 5 Sheets-Sheet 4 WITNESSES: lNVENTOR i fdgard/iE/ gy ATTORNEY Nov. 2, 1943. E, H, R PEGG 2,333,551

ELECTRICAL GAS CLEANING MEANS Filed Feb. 18, 1942 5 Sheets-Sheet 5 WITNESSES: L INVENTOR 0 1 [dWara fl/ffPey a 72 w z LM/Z zaw m'ey ATTOR N EY Patented Nov. 2, I l 943 UNITED STATES PATENT OFFICE ELECTRICAL GAS CLEANING MEANS Edward H. R. Pcgg,

Lakewood, Ohio, assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa.',

Pemisylvania a corporation of Application February is, 1942, Serial No. 431,389

34 Claims.

of difierent substances carried with the gas,-

which is recognized by the art as removable from a gas by such gas-cleaning means; and is hereinafter embracively designated for convenience as dust, dust-particles or the like.

Electrical dust-precipitators of a type to which my invention relates operate on the principle of electrically charging the gas-borne dust-particles and causing the charged dust-particles to migrate to and be precipitated upon dust-collecting electrodes. Dust-collecting electrodes for an aircleaning electrical precipitator usually comprise a plurality of fiat or bent plates which are relatively closely spaced with alternate plates rela-- tively insulated from the intermediate plates between such alternating plates. Such plates are usually continuous over their entire surface, and form boundaries of a gas-stream layer and also of a dust-precipitating field.

The precipitating dust, migrating to the dustcollecting electrodes, tends to accumulate on the electrodes; and continuous efllcient operation of the precipitator requires occasional removal of the collected precipitated dust. However, thorough removal of such dust or dirt from the dustcollecting electrodes has presented a problem to the art; a problem which has not, so far as I am aware, been satisfactorily and economically solved from all viewpoints for systems through which a cleaned air-flow must be constantly maintained.

Experience has shown that for most effective cleaning of the electrodes of an electrical precipitator, especially one having relatively closelyspaced dust-c01lecting plate electrodes, a sulficiently large cleaning force should be applied directly on the collected dirt so that the dirt is forcibly washed oil or removed with an action akin to rapid erosion. A stream of water, played on or between the dust-collecting plates, has been found to be very satisfactory for washing off precipitated dust. The use of water has a further advantage in that it is usually available at suificiently low cost to permit large quantities to be used for cleaning the electrodes. N special means, such as a container, is required to collect or store the water, such as would be the case if a more expensive fluid, such as, for example, a viscous liquid, is used for electrode-cleaning. However, electrical precipitators are frequently built in very large sizes having gas-cleaning means across the large transverse area of the gas-stream, so that it is a practicable difficulty to wash the whole of the gas-cleaning means at one time, or even a good sized portion thereof. Moreover, it is sometimes desirable in some precipitator systems not to interrupt the gas-flow.

Accordingly it is an object of my invention to provide an air-cleaning means of a dust-precipitator system, with means for thoroughly cleaning the dust-collecting elements which does not require stoppage of the air-flow in the gas-duct means of the system; and which does not require stored combustible liquids in, or exposed to, the as-stream.

It is a more specific object of my invention to provide an electrical dust-precipitator system comprising a plurality of gas-cleaning sections fixed in a gas-duct means, each section having a plurality of relatively closely-spaced dust-collecting plate electrodes of some extent in the direction of air-flow, with means for thoroughly cleaning all of the sections without requiring a stoppage of the air-flow in the gas-duct means.

It is an object of my invention to provide a novel practicable automatic means for washing collected dust from the dust-collecting means of a gas-purifying precipitator, or a section thereof, with a stream of water.

It is a further object of my invention to provide a means for washing collected dust or dirt from a gas-cleaning means by successively treating portions or sections thereof, while barring the flow of gas to the portion or section being washed; the portion or section being cleaned being a small enough part of the entire gascleaning means so that the gas cleaning efficiency is not materially affected by diverting the barred gas-stream through the other sections.

It is still another object of my invention to provide a novel practicable automatic means for thoroughly washing a gas-cleaning means comprising a plurality of spaced dust-collecting plates, with a stream of water, then drying the washed plates, and finally spraying or coating the dust-collecting plates with a thin film of viscous liquid (hereinafter called oil) when the nature of the precipitated dust makes it desirable to provide such a film for causing the precipitating dust to stick to the plates, or where the material of the plates makes it desirable to protect them against corrosion or oxidation.

In following my invention, a treating means is provided of smaller size than the gas-cleaning duct means so that it can be made to treat the entire gas-cleaning means. By treating means I mean a device or means which will treat the whole or a part of a gas-cleaning means by washing the dust-collecting elements thereof or otherwise removing the collected dust, ordrying them, or oil coating them, or some analogous treatment or combination of such treatments. Preferably the treating means is made to assume a stationary position in the gas-duct means for treating a portion or section of the gas-cleaning means; and is automatically controlled for carrying out its treating operation or operations. After treating a section, the treating means is moved to another section of the gas-cleaning means so that it can treat that section and so on successively until all the sections of the gas-cleaning means have been treated. In an electrical dust-precipitator system following the teachings of my invention, each section being treated is closed to gas-flow and its charged electrodes deenergized, while the remaining sections are operative so that a gas-flow can be continued through such remaining sections.

In the present preferred embodiment herein described, the treating means comprises an openended framework having fluid-discharging header means reciprocable therein along and across the part or section of the. gas-cleaning means being treated. The front or up stream side of the framework is provided with movable means, such as vanes, operable to bar gas-flow during treating operations. The treating operations for a section require only a few minutes; and during the non-operation of the treating means the vanes may be opened, permitting gas-flow through the treating means and the adjacent downstream gas-cleaning section, so that no extra. transverse space is required in the gas-duct means for the treating means. Treating operations are usually carried out at the end of a time interval which may be a day or week or greater or lesser periods.

Many other objects, features and innovations of my invention, not heretofore specifically mentioned, will be apparent or discernible from the following description thereof, which is to be taken in connection with the accompanying drawings. These drawings are somewhat diagrammatically drawn, with many details eliminated entirely, in the interest of clearness, from some figures or parts of a figure.

In these drawings:

Figure 1 is an elevational view of part of a gas-purifying means showing a treating means, in accordance with my invention, in front of part of an electrical gas-cleaning means;

Fig. 2 is a horizontal sectional view, partly in plan, of the treating means in operative relation to a section of the gas-cleaning means;

Fig. 3 is a side sectional view, partly in elevation, of the treating means in operating relation to a section of the gas-cleaning means;

Fig. 4 is a sectional view of the treating means, looking at it from the upstream side;

Fig. 5 is a schematic representation of part of a gas-purifying electric precipitating system having treating means in its gas-duct means; and

Fig. 6 is a schematic representation, including an electrical diagram, of means for automatically controlling the treating operations of the treating means located in the gas-duct means.

Features of my invention may be applied to electrical gas-purifying dust-precipitators of the combined zone or the separate zone type, by the former meaning a dust-precipitator having a combined or single ionizing and precipitating field in which the dust-particles are both charged and precipitated; and by the latter meaning a dust-precipitator having a separate ionizing field, in which the dust-particles are charged, followed in the direction of gas-flow by a precipitating held for precipitating the previously charged usually comprises a number of units placed side by side in vertical or horizontal rows, or preferably both, and may require a relatively large transverse area of gas-flow tlierethrough, depending on the rated capacity of the system. Gas-cleaning cell-units which may be so arranged side by side to accommodate any practical volume of gas-flow are described in my Patent No. 2,215,298 of September 17, 1940, and in Figure 1 I show diagrammatically such cells arranged in horizontal and vertical relation in a gas-duct means, indicated in its entirety by the numeral 2.

Referring more particularly to Figs. 3 and 5, the gas-duct means 2 is arranged for a substantially horizontal air-flow produced therein by a blower means comprising an electric motor 4 driving a fan 6. The gas-duct means comprises a bottom concrete wall 8, a metallic top wall In and upright metallic side walls 12 and H, the metallic walls being grounded. A gas-cleaning means, indicated in its entirety by the reference numeral I6, is disposed across the air-flow so that air flowing in the gas-duct means passes through the gas-cleaning means.

The gas-cleaning means l6 of the instant embodiment is divided into a plurality of horizontal gas-cleaning sections A, B-M, N, there being any desired number of sections, which are separated by upright partition walls l8 equally spaced across the gas-duct means. In the preferred embodiment of my invention each section A, B-M, N comprises a number of gas-cleaning unit-cells 20, such as shown and claimed in my foregoing Patent No. 2,215,298.

Referring to Fig. 1, each cell 20 comprises an open-ended rectangular casing 22 having opposite long sides 24 and 26 and opposite

short sides

28 and 30. The casing 22 comprises an ionizing zone at the upstream side thereof, comprising a tubular ground-electrode 32 extending between and secured to the

short sides

28 and 30, and insulatedly supporting ionizing-electrodes or -wires 34 between itself and semi-cylindrical ground-electrodes 36 which are united, respectively, with each of the long sides 24 and 26. On the down stream side of the ionizing zone, the casing supports a precipitating zone comprising a dust-precipitating means which is in the form of a plurality of alternately relatively insulated and uninsulated precipitator-electrodes. The relatively uninsulated precipitator-electrodes comprise a plurality of plate-electrodes 38 and the insulated precipitator-electrodes comprise a plurality of plate-electrodes 40. An electrostatic precipitating field is established between adjacent insulated and uninsulated plates for causing dust-particles charged-inthe ionizing zone to migrate to and tend to collect onopposite charged dust-collecting plate-electrodes. For an aircleaning dust-precipitator the plate-electrodes are relatively closely spaced and divide the airstream through the cell into narrow gas-passages.

The gas-cleaning cells, arranged in vertical and horizontal rows, are slightly tilted, as shown in Fig. 3, at an angle to facilitate drainage. In an actual embodiment of my invention, each gascleaning section comprised twenty cells arranged in a horizontal row of five and a vertical row of four cells.

The fan 6 causes an air-flow through the gasduct means in such manner that the air first ,flows through the ionizing zone and then through the precipitating zone.

During the use of gas-cleaning means for removing dust-particles from the flowing air, the dust-collecting plates 38 and 4B tend to accumulate a layer of collected precipitated dust or dirt which should be removed occasionally or periodically. To this end I provide, in accordance with my invention, a treating means for forcibly removing the collected dust from the relatively insulated and uninsulated electrodes of the gascleaning means, and, more particularly, from the dust-collecting plate-electrodes. The treating means is arranged along a face or open-end of the gas-cleaning means, and is of a size ap proximating that of one gas-cleaning section. The treating means has other means, beside washing means, for additional treatment of the electrodes of a section. By moving the treating means from section to section the gas-cleaning means can be entirely washed or otherwise treated. Such a treating means is indicated in its entirety by the reference numeral 42. A single treating means may be used at an open end of the gas-cleaning means, or a pair may be used, one at each open end of the gas-cleaning means.

The treating means comprises an open-ended framework including a substantially rectangular frame 44 of a size approximating the size of a gas-cleaning section. Such a rectangular frame 44 may comprise upright spaced

side walls

46 and 48, a top wall 50 and a bottom supporting. wall 52. The open ends of the frame 44 are aligned with the open ends of the gas-cleaning cells of the gascleaning sections of the gas-cleaning means to permit airflow therethroughout. However, means are provided across the open end of the framework, which is away from the gas-cleaning means, for barring air-flow through the treating means. Such blocking means comprises a plurality of pivotally supported vanes 54 which overlap in closed position. The vanes cooperate with each other and with stationary cross members 56 of the frame 44, to the end that in closed position of the vanes, they overlap each other and the stationary members to bar gas-flow through the treating means. The vanes are operated by any suitable means 60. When the vane-operating means 60 is energizedthe vanes are moved to closed'position and when this means is deenergized, spring means restore the vanes to open position.

Within the frame 44, along the

upright side walls

46 and 48, a pair of T-shaped track and means 86 and 68 movable as a unit, the unit having confining means 69 at each end in sliding engagement with the track and guide means: The header means 66 comprises-a horizontally arranged pipe I0 closed at both ends and provided with a series of spaced fluid discharge spray-nozzles I2. The header means68'comprises a similar but, smaller horizontally arranged pipe I4 having a series of spaced fluid discharge spray-nozzles I6. There are as many or more discharge nozzles 12 and I6 as there are vertical rows of cells in a gas-cleaning section between a pair of successive partition walls I8. The header means 66' is provided with a pipe connection I8 to which is secured a flexible hose 80 connected to pipe means secured to a bridging bar 82 supported by the framework behind a stationary cross member 56 on the upstream side of bar 82. The pipe means includes a rigid pipe 84 passing through the said stationary member 56. For conveying fluid to the header means 68, a similar structure is employed comprising a pipe connection 86, a flexible hose 88 and a short pipe 90 passing through thesame cross member 56. The ends of the pipes 84 and 90 are preferably near the top of the frame 44 and are connected by a flexible hose stretching across the gas-conduit means to accommodate horizontal movement of the cleaning means. Preferably such connections outside the treating means also .pass through the gas-duct means near the top wall l0 so that a suitable loop in such hose connections can be provided to permit the gas-treating means to move across all of the gas-cleaning P sections without any significant amount of pipe or hose resting on the bottom of the gas-duct means, eliminating possible interference with translation of the treating means.

The header means 68 and the header means 66 are secured together in any suitable manner, and the two are reciprocated vertically in the treating means by means of an electric motor guide means 62 and 64 areprovided for guiding the movement of a plurality of movable header driving means and proper mechanical connections. To this end an electric motor I08 is supported on the bottom 52 of the frame 44. The motor I00 may be encased by a housing I82. The

motor drives gearing in a gear box I04 having a shaft I 86 to'which is secured a sprocket wheel I68 meshing with an endless sprocket chain H0 engaging a sprocket wheel H2 secured to an elongated shaft II4 which is across the frame 44. The shaft H4 has secured thereto spaced sprocket wheels which drive spaced sprocket chains H6 and H8 in unison. The sprocket chains H6 and H8 are wrapped around sprocket wheels I20 rotatably mounted at the top of the framework 44. The ends of the chains H6 and I I8 are secured to the header means 66 and 68. One of a the sprocket chains is provided with means for operating a limit switch I22 when the header means reach the top or the bottom of their movements. To this end a sprocket chain H6 may be provided with properly spaced limit switch operating lugs I24 and I26 '(Fig. 6). 'A cable I21 passes through the upper part of'the' gas-duct means to the framework and includes the necessary electrical conductors for the electrical parts in the treating means.

Above the'top wall 56 of the frame 44, the

treating means is provided with a transverse channel I30 having its legs upwardly directed. A plurality of guide wheels I32 are rotatably supported in the channel I30 and ride between spaced guidingangles I34 secured transversely across the top wall III of the gas-duct" means 2.

The bottom of the frame 44 is provided with a pair of spaced wheels I26 and I68 riding in an inverted track-channel I40 which extends transversely across the bottom of the gas-duct means, being supported on a wider channel I42 which encloses a narrower channel I44 resting on the bottom wall 6 of the gas-duct means. The channels I42 and I44 extend across the gas-duct means. The treating means is moved from side to side across the gas-duct along the face of the gas-cleaning means by means of a sprocket chain I50 passing through the side walls I2 and I4 of the gas-duct means and reentering the gas-duct means after passing over a guide sprocket wheel I52 and a driving sprocket wheel I54. Short pipes I56 may be provided about the sprocket chain I50 where they pass through the walls of the gas-duct means, to limit gas-leakage. The lower portion of the sprocket chain I50 rides in the channel I40 and the upper portion has ends secured to the treating means 42 so that rotation of the sprocket wheel I54 moves the treating means 42. a

The treating means 42 is preferably moved so that-it can be substantially aligned with the gascleaning section which it. is to clean, that is, its

side walls

46 and 48 are substantially adjacent a pair of successive partition walls I8, the partition walls preferably extending outwardly from the face of the gas-cleaning cells toward the treating means so as to be capable of being overlappingly engaged by a pair of upwardly directed flaps or vanes I60 pivotally mounted along the downstream edges of the frame sides 46 and 46. These flaps or vanes are operable from the dotted line position shown in Fig. 2 to the full line position by any suitable means, such as, linkages I62 controlled by electrical operating means I64 which, when energized, move the vanes to the full line position. When the operating means I64 are deenergized, springs restore the vanes to the dotted line position. The vanes I60 extend for substantially the height of the adjacent open end of the gas-cleaning means.

A treating means, such as described, may be used to remove collected dust from the gas-cleaning means in different ways.

If it is permissible to shout down or stop the gas-flow in the gas-duct means, the treating means can be moved from section to section manually by an operator entering the gas-duct means through a door I 66, after the gas-cleaning means has been deenergized. With the treating means in association with a gas-cleaning section, the vanes 54 are moved to closed position and the vanes I60 moved into engagement with the associated partitions I6. Latches may be provided to keep the vanes in such positions. Water is then supplied to the pipe which discharges through the nozzles 12 into the cells of the section aligned with the treating means. By movin the pipe 10 up and down in the treating means the entire gas-cleaning section can be cleaned. It is desirable to close the other end of the section being cleanedby any suitable means during such waterwash operation; but in the embodiment shown a second movable treating means 42', similar to the treating means 42, is provided at the other open end of the gas-cleaning means, which can have its vanes moved to enclosing position during the water washing. Sumps I16 are provided in the bottom 8 between the gas-cleaning means and each of the treating means for collecting washing water. Washing water discharged from the header means 66 enters the various cells of the section associated therewith and will quickly flow into a sump I10 at whichever side of the gascleaning means the water discharges. The close spacing of the dust-collecting plates discourages a large discharge of water over the far end of the gas-cleaning means. The sumps I10 are provided with drain pipes I12 at each gas-cleaning section through which discharged water quickly flows into a waste or sewer system external to the gas-duct means, although an external reservoir may also be provided.

After the header has been reciprocated a few times for discharging an abundant quantity of water so that the collected dust is forcibly removed from the cell-units, the water flow can be stopped and an air blast substituted therefor through the header pipe I0 for removing excess water from the gas-cleaning section being cleaned.

After such water-removing, the air blast is stopped and the dust-collecting plates may be coated with a film of oil supplied through the header means 68 and spray discharged thereon through the nozzles I6. Only a small quantity of is ready to be cleaned. When such time arrives,

the gas-flow is again stopped, the gas-cleaning means deenergized and the vanes I60 moved out of engagement with the partition walls I6 (the solid position shown in Fig. 2) enabling the treating means to be moved by the operator to the section selected for cleaning. When the treating means is substantially aligned with this section the vane means I60 are moved into overlapping relation with the partition walls I8, the vanes 64 closed, the water trapping means, comprising vanes 54 of the treating means 42', on the other side of the gas-cleaning means closed and the treating operations previously described repeated.

My invention, however, also contemplates automatic operation of the treating means. To this end a motor I14 drives the sprocket wheels I54 at a suitable speed through a gear box I18. The gear box also drives a combined circuit-controller and position indicator I18 at a predetermined speed in relation to the movement of the sprocket wheels I54. Energy for the motor I14 is upplied from a three phase line I connected to the motor I14 through a reversing switch I62 so that the direction of rotation of the motor can be controlled to permit the treating means 42 and 42' to be positioned adjacent any gas-cleaning section A, B-M, N, in the gas-duct means. The switch I62 may be either manually controlled or automatically controlled.

Each section A, B-M, N is separately electrically energized from a supply line I84 connected through a switch I86 to power-packs I88, I60, I82, I94 etc., for the respective gas-cleaning sections A, B, etc. Each power-pack has a ground connection and high voltage connections I86 and I66 for energizing all of the electrodes of the associated sections. The primary or supply circuit for the power-packs, which may be an ordinary commercial source of alternating-current power, has one conductor 200 common to all the power-packs. The

return conductors

202, 204, 206 and 206 for the power-packs I88, I90, I92 and I94, respectively, are individually provided with individual circuit-interrupters or switches 2I0,

2I2, 2 and 2I6, respectively. Each of the switches 2I0, 2I2, 2I4 and 2I6 is relay controlled through coils 2I8, 220, 222 and 224 for the respective switches. The controller I18 'is provided with cam-operated normally-open control switches A, B'--M, N, respectively associated with the switches. A cam 226 of the controller I18, moves in proportion to the movement of the sprocket wheels I54 and selectively closes the respective switches A, B-M', N.

In normal position of the treating means, with gas-flow through the gas-duct means, the switch to a common return conductor 23I When a gas-cleaning section is to be cleaned, the switch I82 is closed and controlled for causing the motor I14 to move both treating means to this section, the motor I14 simultaneously moving both treating means in unison. The aligned position of the treating means in the gasconduit means can be determined from the position of the control cam 226, which is provided with an arrow and suitable indications. Simultaneously with the closing of the switch I82, the electrical operating means I64 for all vanes I60 are energized thereby causing the vanes to assume a transverse position out of engagement with the partition walls I8, against the action of restoring springs, and permitting the treating means to be moved. When the treating means have been moved by the motor I14 to a desired position, as indicated by the position of the cam indicator 226, the switch I82 is opened stopping the treating means, the cam 226, and deenergizing the electrical operating means I64, permitting the vanes I60 to move to overlapping relation with the partitions I8.

A switch 232 may now be closed for partially completing a coil-energizing circuit through one of these switches A, B'M' or N, which circuit is completely closed by the cam 226 closing the switch associated with the section to be cleaned,

in this case the switch B (Fig. 5). Closure of the switch B completes a circuit through the associated coil 220 thereby raising or opening the switch 2I2 and deenergizing the power-pack I90 associated with the gas-cleaning section B at which the treating means are positioned. Ac-

cordingly, the treating means are now ready for washing this section B.

Referring to Fig. 6, a push-button 234 is closed when the treating means are to treat the associated gas-cleaning section. The push-button 234 controls an obvious energizing circuit for a treating-operation-controlling motor 238 which drives a sequence drum-controller 240 having a plurality of consecutively-ararnged short, adjustable, conducting segments 242,246 and 248, and two

long conducting segments

250 and 252. The drum-controller has a brush 254 adapted to initially engage the segment 242, a brush 256 for engaging the segment 246 and a brush 258 for engaging the segment 248. Brushes 260 and 262 engage the segment 250, and brushes 264 and 266 engage the segment 252 in a separate circuit.

In normal stationary position of the motor 238, the brushes are out of engagement with their associated conducting segments but when the motor is started by closing the push-button 234. brushes 260 and 262 engage conducting segment 250 and brushes 264and 266 engage conducting segment 252 for a complete cycle of operation of the drum-controller 240; whereas the

brushes

254, 256, and 256 successively engage the conducting

segments

242, 246, and 248 respectively, for adjustable time periods, the conducting segment 242 interrupting the circuit to the brush 254 shortly before the brush 256 engages the segment 246; and the brush 258 engaging the segment 248 when the segment 246 is about to leave, or has left,.the brush 256.

Closing of the push-button 234 starts the motor 238 which operates the drum controller 240 through its cycle of control. The push-button need not be held closed more than a moment because the drum controller closes a circuit, branching the push-button, from the power conductor 261, a conductor 268, brush 260, segment 250, brush 262 and conductor 210 connected to the motor 238. The circuit passes through the motor to the other power conductor 269. The segment 250 is long enough to maintain this circuit completed until the drum-controller is returned to its initial starting position where all the brushes are disengaged from the conducting segments. An obvious circuit, across the motor 230, energizes all vane-operating means 60 as long as the motor 238 is energized, and forces the vanes 54 to closed position against the action of their restoring spring or springs.

When the drum-controller starts to rotate a control means for the energizing circuit for the motor I00 of a treatingmeans, Which reciprocates the associated header means 66 and 68, is completed from a power conductor 212 of threephase power lines; this circuit including brush 264, conducting segment 252, brush 266, a conductor 214, a reciprocable switch-arm 216 of the limit switch I22 of the treating means, a switchcontact 218 in engagement with the switch arm 216, a conductor 280 and a coil 290 of a relay 292; the circuit being completed through conductor 294 to another phase 296 of the three-phase power supply, Energization of the relay coil 290 causes relay contactors 298 to complete the circuit of 'the

power conductors

212 and 296 to such motor I00, which starts to rotate in a certain direction. The switch-operating lug I26 leaves switch-arm 216 which, however, remains in engagement with the switch-contact 218.

After the header means 66 and 68 have reached a limit of their movement, the limit-switch operating member or lug I24 engages the switch- .arm 216 to cause it to leave the switch-contact 218 and engage a switch-contact 300. This deenergizes' the coil 290 of the relay 292 and energizes a coil 302 of the relay 304 to reverse the phase connections of the

power conductors

212 and 296 for causing such motor I00 to again reverse its direction of rotation, the switch-arm 216 remaining in contact with the switch-contact 300 until the other limit-switch operating lug I 26 moves the switch-arm to the other switchcontact 216 when the header-means reach the other end of their travel, thereby again changing the direction of rotation of the motor I00. In this manner the header means are continuously reciprocated back and forth so long as the circuit including the brushes 264 and 263 is closed through the conducting segment 252, this segment being preferably as long as segment 250.

The

segments

242, 246 and 243 represent treating operation control means. When a circuit is completed from the power conductor 261, through conductor 263, brush 260, segment 250, a ,connector conductor 306, segment 242, brush 254, a

,solenoid coil 303 and conductor 3I0 to the other power conductor 263, a water-valve 3I2 is opened through energization of the solenoid 303, permitting water under pressure, which may be the customary pressure of available water-supply means, to flow from a water supply outside the gas-duct means, through the valve 3I2, a pipe 3I3, passing through a wall I2 of the gasduct means, through the flexible pipe loop connected to the pipe 84 and the pipe loop 80, and be discharged through the nozzles 12 of the header means 66, thus washing the electrodes of the associated gas-cleaning section. Water is discharged through the header means 66 while it is reciprocating in the framework 44. After a suitable time the brush 254 leaves the segment 242, deenergizing the coil 303 so that the flow of water is stopped.

The brush 256 then engages the segment 246 completing an obvious circuit to a solenoid 3I4 which electrically controls a valve 3I6 in an air supply pipe 3I3 connected to the common pipe 3I3 which is part of the pipe-connections to an end of the pipe 34, for conveying fluid to the header means 66. Opening of the valve 3; causes an air blast discharge through the nozzles I2 so that excess water in the gas-cleaning section being treated is rapidly removed. The air supply may be a source of air under pressure, which air already has been cleaned by the precipitator. The liquid drops carried by the air impinges on the vanes and the other gas-flow obstructions of the treating means, and are thereby caught. After a suitable time-interval for removing the excess water, the brush 256 leaves the segment 246, and the brush 258 engages the segment 243. Interruption of the circult including the solenoid 3I4 closes the valve 3I6 to stop the air blast through the header means 66; and the brush 253 and segment 248 complete a circuit to an oil pumping motor 322 which drives an oil pump 324 to supply oil under pressure to the header means 68, the oil being spray discharged through the nozzles I6 of the header means 63, onto the dust-collecting plates of the section being treated. The oil pump pumps oil from a container outside the gas-duct means.

After suitable spraying, the drum-controller reaches its original starting position where all brushes are disengaged from'the conducting segments. Consequently, the holding energization circuit for the motor 233 and for all of the electrical vane-operating means 60, which passes through the brush 262, is deenergized, thereby stopping the drum controller 240 and permitting the vanes 54 to assume an open position for airflow through the treated section. After this treating operation has been completed, the switch 232 may be opened thereby interrupting the energizing circuit through the cam closed switch B for the relay coil 220. This permits the powerpack I32 for the gas-cleaning section B, which has just been treated, to be reenergized. However, I prefer to incorporate the equivalent of the switch 232 on the drum-controller 240 by means of a conducting segment 326 engageable by a brush 323 in all positions of the drum controller except in the stationary position thereof. The

conductors

330 and 332 for the brush 323 and segment 326, respectively, corresponding to the conductors 330' and 332' for the switch 232 of Fig. 5. By providing the equivalent of the switch 232 on the drum-controller 240 which times the operation of such a switch, the gas-cleaning section being treated is deenergized and the vanes 54 closed only so long as the treating means is carrying out its treating operations.

While a section is being cleaned, it is evident that the other sections of the gas-cleaning means are energized and an air-flow passes through them because the blower motor 4 is energized through a circuit including the power conductors I84 and door-operated switch 230 operated by the door I66.

Preferably, but not necessarily, the gas-cleaning means is divided into sufiiciently small sections to insignificantly aflect the gas-cleaning eiliciency of the precipitator when the gas-flow through a section is barred and diverted through the remaining sections.

With the vanes 54 oi. both treating means closed and all the flap-vanes I60 engaging the partition walls I3,-air-flow through the associated gas-cleaning section is negligible. The various channels I30, I34, I40, I42, introduce a highly restricted gas-flow path; and since only about 16% of the gas can normall pass through a section of a six-section gas-cleaning means, any small leakage through the treating means with the vanes closed is an insignificant proportion of the total gas-flow volume.

A single switch means 3 with associated relays, and a single drum-controller 240 are sufficient to control the treating operations of both treating means; and I have explained the control for a single treating means in the interests of brevity. The electrical control circuits for the other treating means can duplicate those shown and explained, as for example by additional parallelly-connected conductors connected to the

brushes

254, 256 and 253 for controlling duplicate solenoid-controlled fluid valves for the other treating means, and a conductor connected to the brush 264 for controlling the energization of the header-driving motor of the other treating means, in a manner well known to one skilled in the art.

However, the header means for one treating means is provided with a driving connection between its motor I00 and its header means for reciprocating such header means at a rate slightly difierent from that of the header means of the other treating means so that the oppositely-directed discharged fluids will cross at different places vertically along the gas-cleaning section being treated. The closed vanes 54 and the vanes I60, in contact with the partition walls I3 of both heating means, substantially encase the section being treated and prevent sprayed or discharged liquid from entering the gas-flow in the gas-duct means.

A switch 340 in a connection 342 permits the oil pumping motor 322 to be hand-operated; and suitable hand-operated valves and supply pipes may be provided for manual control of the fluid supply to the header means.

While I have described my invention in a specific form, it is obvious that many equivalent constructions and features may be substituted. and modifications made therein.

I claim as my invention:

1. An electrical dust-precipitating system for cleaning a gas-stream, comprising gas-duct means for the gas-stream; gas-cleaning means for charging and precipitating dust-particles of said gas-stream; said gas-cleaning means comprising a plurality of gas-cleaning sections, each section having a plurality of spaced dust-precipitating plate-electrodes for collecting dust; liquid flushing means operable, at times, for discharging a liquid between the dust-precipitating electrodes of a section, means for causing said liquid-flushing means to be operable for cleaning difierent ones of said sections at different times; and means for substantially enclosing a section being cleaned in a manner to prevent significant gas-flow therethrough while there is a, gas-stream through said gas-duct means, and to prevent flushing liquid from flowing with the gas-stream.

2. An electrical dust-precipitator system for cleaning flowing gases by electrically charging gas-borne dust-particles and precipitating charged dust-particles; comprising gas-duct means for a gas-stream; gas-cleaning means across the gas-stream path for charging and precipitating gas-borne dust-particles, said gascleaning means comprising a plurality of sections, each section having a plurality of relatively closely-spaced dust-precipitating plate-electrodes upon which precipitated dust-particles collect; means for causing a flow of gas through said gasduct means; electrode-cleaning means operable, at times, for removing collected dust from the dust-precipitating plate-electrodes of a section by discharging a fluid into the spaces between the plate-electrodes thereof, means for causing a successive cleaning of difierent sections by said electrode-cleaning means, and movable means for causing gas-flow through the section being cleaned by said electrode-cleaning means to be substantially barred while gas is flowing through the gas-duct means.

3. An electrical dust-precipitator system for cleaning flowing gases by electrically charging gas-borne dust-particles and precipitating charged dust-particles; comprising gas-duct means for a gas-stream; gas-cleaning means across the gas-stream path for charging and precipitating gas-borne dust-particles, said gascleaning means comprising a plurality of sections, each section having a plurality of relatively closely-spaced dust-precipitating plateelectrodes upon which precipitated dust-particles collect, said plate-electrodes being adapted to parallel the gas-flow; means for causing a flow of gas through said gas-duct means; electrodecleaning means comprising fluid-nozzle means, operable, at times, for removing collected dust from the dust-precipitating plate-electrodes of a section by discharging a fluid into the spaces between such plate-electrodes, means for causing a successive cleaning of difierent sections by said electrode-cleaning means, movable means for causing gas-flow through the section being cleaned by said electrode-cleaning means to be substantially barred, while gas is flowing through the gas-duct means, fluid-supply pipe means connected to said fluid-nozzle means, passing through said gas-duct means, and fluid-removing means for removing discharged fluid from said gas-duct means substantially as soon as the discharged fluid has performed its cleaning function.

4. A gas-purifying electrical precipitator system comprising gas-duct means for a gas-stream, gas-cleaning means in said gas-duct means across the gas-stream, comprising an ionizing means and a dust-precipitating means successively in the direction of gas-flow, said ionizing means comprising cooperating ionizing and non-discharging electrodes, said dust-precipitating means" comprising a plurality of relatively uninsulated and insulated precipitating-electrodes paralleling the gas-flow, electrode-treating means operable, at times, for treating a portion or said ionizing and non-discharging electrodes and precipitating-electrodes, means for causing said electrodetreating means to be operable successively on different portionsof said electrodes, blocking means for preventing a significant gas-flow through the portion of said gas-cleaning means of which the electrodes are being treated by said electrodetreating means when there is a significant gasflow through other portions of said gas-cleaning means, said blocking means being operable for permitting a gas-flow through all portions of said gas-cleaning means during non-operation of said electrode-treating means, and means for energizing only the electrodes of the portions of said gas-cleaning means through which there is a significant gas-flow.

5. Equipment for removing dust-particlespfrom a flowing gas-stream, comprising gas-duct means for the gas-stream, stationary gas-cleaning means in said gas-duct means across the gas-stream, treating means adjacent said gas-cleaning means operable for treating a portion of said gas-cleaning means and blocking gas-flow through such portion, means for moving said treating means to fixed positions adjacent different portions of said gas-cleaning means, and automatic means for causing said treating means to be operable for a predetermined time in each fixed position.

6. An electrical dust-precipitator system for electrostatically cleaning a gas-stream by electrically charging-gas-borne dust-particles and precipitating charged dust-particles, comprising gasduct means having a plurality of open-ended gascleaning sections arranged side by side across the gas-stream, each of said sections having ionizing means for charging dust-particles and plateelectrodes for precipitating charged dust-particles, means for simultaneously energizing all the ionizing means and the plate-electrodes of the respective sections, a treating means in preset spaced relation adjacent an open end of one of said sections, operable for removing collected dust from the ionizing means and plate-electrodes of such section, means for moving said treating means from section to section whereby each section may be treated, and means associated with said energizing means for deenergizing for a period only the ionizing means and plateelectrodes of the section associated with said treating means.

'7. An electrical dust-precipitator system for electrostatically cleaning a gas-stream by electrically charging gas-borne dust-particles and precipitating charged dust-particles, comprising gasduct means having a plurality of open-ended r stationary gas-cleaning sections arranged side by side across the gas-stream, each of said sections having ionizing means for charging dustparticles and plate-electrodes for precipitating charged dust-particles, a treating means in preset spaced relation adjacent an open end of one of said sections operable for removing collected dust from the plate-electrodes of such section and for blocking gas-flow through such section during such dust-removal, means for moving said treating means from section to section for separatelytreating the sections, means for operating said treating means, and means for energizing the ionizing means and plate-electrodes of the respective sections, the last said means including means for deenergizing' the plate-electrodes of a section being treated by said treating means but adapted to reenergize the plate-electrodes after treatment and while-the treating means is associated with such section.

8. Equipment for removing dust-particles from a flowing gas-stream, comprising gas-duct means for the gas-stream, means for causing a gas-flow through said gas-duct means, stationary gas-cleaning means comprising a plurality of juxtaposed individual gascleaning sections across the gas-stream path for collecting dust from the gas-stream, said gas-cleaning means comprising spaced wall means defining such gascleaning sections, dirt-removing means for removing collected dust from said gas-cleaning means, comprising treating means operable for cleaning said gas-cleaning sections, one at a time, with a dirt-removing fluid, and means comprising operable means movable ior association with said wall means for substantially barring gas-flow through the gas-cleaning section being cleaned by said treating means while there is a gas-flow through said gas-duct means, said operable means being movable from association with said wall means for permitting a gas-flow through the last' said section.

9. Equipment for removing dust-particles from a flowing gas-stream, comprising gas-duct means for the gas-stream, open-ended stationary gas-cleaning means across the gas-stream path for collecting dust-particles from the gasstream, liquid-discharging means transverse to the gas-stream along an open end of said gascleaning means, for discharging a liquid for removing collected dirt from said gas-cleaning means, said liquid-discharging means being operable successively on difierent portions of said gas-cleaning means, movable means operable for temporarily blocking gas-flow through the portion of said gas-cleaning means being cleaned and to stop discharged liquid from travelling beyond the gas-cleaning means, and drain means for conducting sucirdischarged liquid out of said gas-duct means.

10. Equipment for removing dust-particles from a flowing gas-stream, comprising gas-duct means ior the gas-stream, means for causing a gas-flow through I said gas-duct means, gascieaning means comprising a plurality of juxtaposed individual stationary gas-cleaning sections across the gas-stream path for collecting dust from the gas-stream, said gas-cleaning means comprising spaced wall means defining gascleaning sections, flushing means for flushing said gas-cleaning sections, one at a time, with a dirt-removingfliquid, means for substantially barring gas-flow through the gas-cleaning section being flushed by said flushing means while there is a gas-stream flowing through said gasduct means, and means associatable with said wall means for stopping dirt-removing liquid flushing a gas-cleaning section, before such liquid can be carried along by the gas-stream.

11. An electrical dust-precipitator system for electrostatically cleaning a gas-stream by electrically charging gas-borne dust-particles and precipitating charged dust-particles, comprising gas-duct means having a plurality of open-ended gas-cleaning sections arranged side by side across the gas-stream, each of said sections having ionizing means for charging dustparticles and plate-electrodes for collecting charged dust-particles, means for separately energizing the ionizing means and the plate-electrodes of the respective sections, a treating means in preset spaced relation adjacent an open end of one of said sections for washing collected dust from such section, means for moving said treating means successively from section to section, and means for indicating outside said gas-duct means the position of said treating means in said gas-duct'means.

12. An electrical dust-precipitator system for electrostatically cleaning a gas-stream by electrically charging gas-borne dust-particles and precipitating charged dust-particles, comprising gas-duct means for a gas-stream, gas-cleaning means across the gas-stream path for electrically removing dust-particles from the gas-stream, said gas-cleaning means comprising a plurality of relatively closely-spaced plate-electrodes upon which such dust-particles collect, an electrode-treating means for treating a portion of said gas-cleaning means, means in said gas-duct means for supporting said electrode-treating means in transverse relation to the gas-stream, spaced from but near a boundary of said gascleaning means, for guided movement successively to diiierent portions of said gas-cleaning means, said electrode-treating means comprising means for discharging liquid between the plate-electrodes of the portion of said gas-cleaning means, which is then associated with said electrode-treating means.

13. An electrical dust-precipitator system for electrostatically cleaning a gas-stream by electrically charging gas-borne dust-particles and precipitating charged dust-particles, comprising gas-duct means, means for causing a gas-stream to flow through said gas-duct means, gas-cleaning means across the gas-stream path, said gascleaning means being divided into a plurality of stationary individual sections, each section comprising a plurality of relatively insulated and uninsulated electrode-means, treating means comprising treater mean in the pathoi the gasstream, operable for treating said sections, one at a time, for a time interval, and means for diverting the gas-stream from the section being treated and the treater means treating such section, and operable for permitting gas-flow through all of the sections of said gas-cleaning means when said treater means is not operating for treating a section of said gas-cleaning means.

14. An electrical dust-precipitator system for electrostatically cleaning a gas-stream by electrically charging gas-borne dust-particles and precipitating charged dust-particles, comprising gas-duct means, means for causing a gas-stream to flow through said gas-duct means, gas-cleaning means across the gas-stream path, said gascleaning means being divided into a plurality of sections, each section comprising a. plurality of relatively insulated and uninsulated electrodemeans, treating means operable for successively treating said sections, comprising water-washer permitting gas-flow through such section it is not being treated.

15. Equipment for removing dust-particles from a flowing gas-stream, comprising gas-duct means for the gas-stream, gas-cleaning means in said gas-duct means'across the gas-stream, treating means adjacent said gas-cleaning means when operable for successively water-washing and oil-spraying a portion of said gas-cleaning .means, means for moving said treating means to fixed positions adjacent difierent portions 01' said gas-cleaning means, and automatic means for causing said treating means to water-wash for a predetermined time period an adjacent portion of the gas-cleaning means, and to oil-spray position inside said gas-duct means adjacent diflerent portions of said gas-cleaning means, and treater means,associatable with said structure in such stationary position for treating the associated portion of said gas-cleaning means with a plurality of different fluids including liquid, means comprising a single pipe-connection passing through a wall of said gas-duct means to said treater means, and control means for causing one of said plurality of fluids at a aasass associated edge oi said dust-collecting plates,

whereby the entire gas-cleaning device may be cleaned, said moving means repeatedly reciprocating said spray means so that they cross each other at diflerent places along said gas-cleaning device, said spray means being adapted to discharge plate-washing liquid for washing collected dirti'rom said plates.

19. An electrical dust-precipitator system for electrostaticalLv cleaning a gas-stream by electrically charging gas-borne dust-particles and precipitating charged dust-particles, comprising gas-duct means having gas-cleaning means across the gas-stream path, said gas-cleaning means comprising a plurality of relatively closeily spaced alternately relatively insulated and uninsulated electrode-means comprising a plurality of spaced dust-collecting plates, water-washer means'along a boundary of said gas-cleaning means operable for a time interval for washing collected'dust from a number 01' said plates by discharging water between said plates, gas-blast means along a boundary of said gas-cleaning means operable for a time interval after operation of water-washer means, for directing a blast of gas onto the water-wetted plates, for decreasing the water on such plates, spray means opertime to pass through said single pipe-connection,

17. An electrical dust-precipitator system for electrostatically cleaning a gas-stream by electriended gas-cleaning sections arranged side by side substantially transversely across the gas-stream path, track means in said gas-duct means along an open end of said gas-cleaning means but spaced slightly therefrom, an open-ended framework ridable on said track means, of a size for association with each of said gas-cleaning sections, means for moving said framework for successive association, in fixed position, with each of said gas-cleaning sections, each of said gascleaning sections comprising ionizing electrodemeans for charging gas-borne dust-particles and dust-precipitating electrode-means for collecting charged dust-particles, means for electrically energizing the electrode-means of the respective gas-cleaning sections, means 'operablefor substantially enclosing said framework and any associated one of said gas-cleaning-sections, means in said framework operable for washing the associated one of said gas-cleaning sections, and

means for deenergizing the electrode-means of such associated one .of said gas-cleaning sections.

18. Equipment for removing dust-particles from a flowing gas-stream, comprising gas-duct means for the gas-stream, a gas-cleaning device comprising a plurality of spaced dust-collecting plates across the gas-stream, paralleling the gasstream, plate-cleaning means along an edge of said dust-collecting plates, plate-cleaning means along an opposite edge of said dust-collecting plates, each of said plate-cleaning means comprising spray means for discharging plate-cleaning liquid into a portion of the spaces between said dust-collecting plates, and moving means for moving each of said spray means across the able for a time interval after operation of said gas-blast means, for spraying'a viscous film upon such-plates, and means for substantially stopping the said gas-stream only through said number of plates while they are being successively so treated.

20. An electrical dust-precipitator system for electrostatically cleaning a gas-stream by electrically charging gas-borne dust-particles and precipitating charged dust-particles, comprising gas-duct means having gas-cleaning means across the gas-stream path, said gas-cleaning means comprising a plurality of relatively closely-spaced alternately relatively insulated and uninsulated electrode-means comprising a plurality of spaced dust-collecting plates, liquid-washer means along a boundary of said gas-cleaning means for washing collected dust from a portion of said plates by discharging liquid between said plates, gasblast means along a boundary of said gas-cleaning means, operable after operation of the liquidwasher means, for directing a blast of gas onto the liquid-wetted plates, for decreasing the liquid on said plates, and liquid-catching means for discharged liquid and liquid drops carried by said gas-blast.

' 21. An electrical dust-precipitator system for electrostatically cleaning a gas-stream by elec-- trically charging gas-borne dust-particles and precipitating charged dust-particles, comprising .means for spraying a viscous film upon such electrode-means, means for operating said spraying means for a time interval after operation of said water-washer means; and means for diverting the gas-stream from the section being treated, while there is a gas-flow through said gas-duct means:

" 22. An electrical dust-precipitator system for electrostatically cleaning a gas-streamby elec-' trically'charging gas-borne dust-particles and precipitating charged dust-particles comprising gas-duct means having gas-cleaning means across-the gas-Stream path, said gas-cleaning means being divided into-a plurality of sections,

each section-comprising a limited number of gascleaning cells comprising relatively closelyspaced alternately relatively insulated and uninsulated plate-electrodes; means for successively treating said sections,"comprising water-washer means insaid gas-duct means for washing collected'dust from the plate-electrodes of the cells of a section being treated by discharging water onto such plate-electrodes, means for operating said" water-washer means for a time interval, means for spraying a viscous film upon the plateelectrodes of the cells of a clean washed section, means for operating said spraying means for a time-interval after operation of said water-washermeans; means for diverting the gas-stream from the cells-of a section being treated, and means for permitting gas-flow through the last said cells when said treater-means is associated therewith but is not operating for treating such cells.

'23. Equipment for washing collected dust removed from a gas-stream by gas-purifying means of a type described, comprising an open-ended framework through which the gas-stream may pass, header means supported by said framework movable back and forth in said framework for discharging a washing fluid away from one end of said framework, and movable means for opening and closing the other end of said framework respectively to permit and bar gas-flow.

24. Equipment for washing collected dust removed from a gas-stream by gas-purifying means of a type described, comprising a walled framework having an open end, means supported by said framework for discharging a fluid away from said end of said framework, retractable means along an edge of said framework at said open end thereof for, in effect, extending a wall of said framework in the general direction of said fluid discharge.

25. An electrical dust-precipitator system for electrostatically cleaning a gas-stream by electrically charging gas-borne dust-particles and precipitating charged dust-particles comprising a gas-cleaning means having dust-charging and precipitating means including electrodes for collecting precipitated dust, said gas-cleaning means having spaced walls projecting beyond said dust-charging and precipitating means, means for removing collected dust from said electrodes, comprising a movable framework in spaced relation to edges of a pair of said walls, movable vane means for closing the space between said framework and said edges of said walls, and means for movably supporting said vane means to enable the framework to be moved.

26. An electrical dust-precipitator system for electrostatically cleaning a gas-stream by electrically charging gas-borne dust-particles and cleaning means, means in said gas-duct means for supporting said electrode-treating means transverse to the gas-stream spaced from but near a boundary of said gas-cleaning means for guided movement successively to difl'erent portions of said gas-cleaning means, said electrodetreating means comprising spray means for discharging sprayed liquid between the plate-electrodes of the portion of said gas-cleaning means, which is their associated with said electrodetreating means, said spray means comprising water flush means for flushing collected dust from said plate-electrodes, and means for catching and draining the flushing water containing the flushed-ofl dust.

- 27. An electrical dust-precipitator system for duct'means for successive stationary associationwith each of said gas-cleaning sections, means in said framework for discharging a cleaning fluid for cleaningthe section with which the framework is associated, and means for closing the end of said framework away from the said last-mentioned section.

28. An electrical dust-precipitator system for electrostatically. cleaning a'gas-stream by electrically charging gas-borne dust-particles and precipitating charged dust-particles, comprising gas-duct means for a gas-stream, open-ended gas-cleaning means comprising a plurality of open-ended gas-cleaning sections arranged side by side substantially transversely across the gasstream path, a framework movable in said gasduct means for successive stationary association with each of said gas-cleaning sections, and fluiddischarging means movable from side to side in said framework, said fluid-discharging means comprising a, plurality of nozzle means for discharging a cleaning fluid toward the section with which the framework is associated.

29. Equipment for removing collected dust removed from a gas-stream by gas-purifying means, comprising a framework having an open end defined by walls comprising a pair of spaced substantially, parallel sides, means for' closing the other end of said framework, header means in said framework extending between said spaced sides, said header means comprising nozzle means for discharging a fluid away from and across said open end of said framework, means for supporting said header means for guided movement back and forth along said spaced sides, electric motor driving means supported by said framework, including driving mechanism in said framework for moving said header means, and energizing means for said electric motor driving means, comprising control means operable at the limits of movement of said header means for reversing said electric motor driving means to reverse the movement of said header means.

30. Equipment for removing dust-particles from a flowing gas-stream, comprising gas-duct means for the gas stream, a stationary gas-cleaning means extending across the gas-stream, said gascleaning means comprising a. first side and a different open side through which gas may flow, gas-impervious wall means extending in a gasstream direction and dividing said gas-cleaning means into a plurality of adjacent crosswise arranged sections, treating means operable along said first side for separately cleaning diflerent of said sections at different times while there is a gas-flow in said gas-duct means, and means, cooperable with said wall means, operable for blocking significant gas-flow through a said section being cleaned, the last said means being operable to permit gas-flow through the last said section after treatment by said treating means.

31. A gas-purifying electrical precipitator system comprising gas-duct means for a gas-stream, stationary gas-cleaning means in said gas-duct means, across the gas-stream, comprising a plurality of spaced relatively uninsulated and insulated electrode means for precipitating charged dust particles in the gas-stream, movable electrode-treating means having fluid-nozzle 1 means, operable for association with different sections of said electrode means for separately treating the respective sections of said electrode means through the medium of liquid discharged from said fluid-nozzle means towards said electrode means, fluid supply-pipe means connected-to said fluid-nozzle means, passing through said gas-duct means, and barrier means for stoppingdischarged liquid and causing it to drain from said gas-duct means, whereby such liquid is prevented from being carried along by the gas-stream.

32. A gas-purifying electrical precipitator 'sysportions 01' said gas-cleaning means,.liquid-dis- 1 charge means carried by said framework, for discharging a plate-cleaning liquid between the plate electrodes or the portion of the gas-cleaning means with which the framework is, at the time, associated, and liquid-catching means operable for preventing discharged liquid from flowing with the gas-stream, said liquid-catching means 5 having means operable at the other end of the portion of the gas-cleaning means with which the framework is, at the time, associated.

33. An electrical dust-precipitator system for electrostatically cleaning a gas-stream by electril0 cally charging gas-borne dust-particlesand precipitating charged dust-particles, comprising gasduct means having a plurality of open-ended gascleaning sections arranged side by side across the gas stream, each of said sections having ionizing means for charging dust-particles and plate-electrodes for collecting charged dust-particles, means for separately energizing the ionizing means and the plate-electrodes of the respective sections, a, treating means in preset spaced relation adjacent an open end of one of said sections for washing collected dust from such section, means for moving said treating means successively from section to section in similar spaced relation for individual washing of the sections,

and means outside said gas-duct means for con- 'trolling the position of said treating means.

34. An electrical dust-precipitator system for electrostatically cleaning a gas-stream by electrically charging gas-borne dust-particles and precipitating charged dust-particles, comprising gasduct means having a, plurality of open ended gascleaning sections arranged side by side across the gas-stream, each c! said sections having ionizing means for charging dust-particles and plate-electrodes for collecting charged dust-particles,

means for separately energizing the ionizing means and the plate-electrodes of the respective sections, a treating means in preset spaced relation adjacent an open end of one of said sections for washing collected dust from such section, means for moving said treating means successively' from section to section in similar spaced relation for individual washing of the sections, and means outside said gas-duct means for controlling the position and the washing operations oi said treating means.

. EDWARD H. R. PEGG.