US1968334A - Water film precipitator - Google Patents

Description

July 311., 1934. A. N. CROWDER ET AL WATER FILM PRECIPITATOR Filed July 13, 1932 ZSheets-Sheet l III!!! y 31, 934. A. N CROWDER ET AL 1,968,334

WATER FILM PRECIPITATOR Filed July 13, 1952 2 Sheet-Sheet 2 Patented July 31, 1934 PATENT OFFICE WATER FILM PBECIHTATOB Alexander N. Crowder, Brldgewater Township,

Somerset County,

and Robert B. Hesson,

Bound Brook, N. 1., assignors to Research Cor poration, New York, N. Y., a corporation of New York Application July 13,1932, 86H! m. mass is Claims. (01. 183-7) This invention relates to electrical precipitators of the Cottrell type for removing suspended particles from gases, and particularly to precipitators in which a 'film of liquid is maintained on the sur- Y 5 faces of the collecting electrodes while the apparatus is in operation.

The object of the invention is to provide a pre-v cipitator with liquid washed collecting electrodes and means with which it is possible to maintain 1 a continuous film of liquid over the entire surface .upon which suspended material is collected.

More particularly the object of the invention is to provide a precipitator in which it is possible to maintain upon every part of the collecting sur- 1 face a water film of uniform depth which may be and preferably is extremely thin. Another object of the invention is to provide means for controlling the flow of liquid over the collecting surfaces in a positive manner and for making possible a redistribution of the liquid at any time misalignment of the parts or other changes make such redistribution necessary. Still another object of the invention is to provide a precipitator having collecting electrode units which are relatively adjustable so that each can be positioned to receive its proportionate amount of washing liquid from a common supply.

Another object of the invention is to construct the top edge of the collecting electrode as a weir over which a washing liquid can be made to flow and to provide means whereby the height of the weir can be altered. A more particular object of the invention is to provide a precipitator com prising a frame, a header supported by the frame,

a collecting electrode projecting into the header through a flexible gas and liquid tight joint, and means'for altering the height of the collecting electrode with respect to the header.

. The advantages that can be derived from providing a liquid film on the collecting electrodes of an electrical precipitator of the Cottrell type have been known for many years, but few operators of precipitators at this time are making use of water or other liquid films and securing the advantages which they-provide, for the reason that it is difficult to embody this feature in precipitators in a practical manner.

, When water, for instance, is projected upon a surface in sufficiently-large quantities, the total surface will, of course, become covered with the water, but the use of large quantities of water has definite disadvantages. The expense is great, the disposal of the water presents problems, and great care must be taken in supplyin the water 66. to the collecting electrodes and removing it again because arcing to the electrodes of opposite polarity is apt to'take place when the quantity of water .in use is considerable.

when attempts have been made to reduce the amount of water, the results have invariably been unsatisfactory. Sprays have been used but seldom do they distribute water uniformly, and when several sprays are used in parallel the different units seldom supply equal amounts of water, or if this condition is secured initially. clogging of the spray nozzles causes unequal distribution and eventually causes a shut down of the apparatus until the spray nozzles can be cleaned.

This invention has to do with improvements in apparatus and methods which overcome such dis- 7 I advantages as those just described and. make possible the use of liquids for carrying away the material removed in an electrical precipitator in an efllcicnt and practical manner. The invention can be well illustrated as applied to a precipitator 78'- comprising vertical pipes for collecting electrodes and a rod or wire. axially suspended in each pipe functioning as discharge electrodes. The tops of the pipes are formed as weirs over which the liq uid, for instance water, flows. This use of the 80 pipe tops and the other elements of the invention are best understood by referring to the accompanying drawings, in which: 7

Figure 1 shows in elevation, partly in section on the line 1-1 of Fig. 2. a precipitator em- 86 bodying the invention;

Figure 2 is a plan view of the precipitator shown inFigurel;

isasectionofFigureltakenst Figure 3 3 -3;

Figure 4 is a sectional elevation of one of the collecting (pipe) electrodes of the precipitator shown'in Figure 1:

Figure 5 is a plan, partly in section. onlinc' 5-5 of Figure 4;

Figure 6 shows in some detail a prefemd means for controlling-the water as it is used with the invention; and

Figure '1 shows in sectionslelevation an alternative construction which can be used at the top of the collecting pipes for leveling purposes.

Figures 8, 9and10 show a vertical section. a

plan view and a detailed section of another modiflcation of the invention.

n Figures 1, sand 3. the shell or casingof 106 the precipitator. designated by numeral 1, is

supported by structural members 2. The gas to be cleaned'is made to enter the shell through inlets 3 and leaves the shell throush outlets 4. The

collecting electrodes are pipes designated by 5, 110

did

art has found suitable for such use. The discharge electrodes are suspended from members 7, which are in turn supported by bus bars 8' which rest upon insulators 9. Where the discharge electrodes 6 emerge from the bottom of pipes 5, a shroud 10 is preferably placed over each of them to diminish the likelihood of arcing because the electric field is concentrated at this point and the presence of dripping liquid still further distorts the electric field at the bottom of the pipes. Weights 11 hold the discharge electrodes taut and a steadying frame 12 spaces them and minimizes the possibility of their swaying. The collecting electrodes 5 are supported upon top header plate 13 which rests upon membars 14, which in turn are supported by substantial structural members as shown at 15. Just above the bottom of pipes 5 there is a lattice work for positioning the pipes. It is made up of bars 16 and 17, through. which screws or bolts 18 project to press against the sides of the pipes as shown. The pipes can be plumbed by turning the screws. Lock nuts 19 secure the screws in definite position.

To provide water for washing the inner surfaces of the pipes, the space about the top of the pipes, which projects above header plate 13, is used as a trough or pond. Water is continuously supplied to this space and the top edges of the pipes, functioning. as weirs, cause the water to remain at a definite height in the pond, depending upon the rate at which it is supplied. The excess as supplied flows over the weir tops and down the inner surfaces of the pipes. It is readily appreciated that the more closely all the pipe tops are held at the same level, the more evenly will be the distribution of thewater to the several pipes. The top header is made water tight in a manner to be later described and is divided into a plurality of troughs or ponds by barriers 26.

The reason for dividing the header is to make it unnecessary to raise every pipe to exactly the same level-the level of a single extended pond of water. To go back and forth over say 200 pipes until every one is exactly the same height and receiving the same amount of water is a difficult task; and ii, at a later time, the shell gets out of plumb but slightly, the height of pipes on opposite sides of the apparatus will be sumciently altered to necessitate re-alignment of pipes. With the top header divided into several ponds the liquid in the various ponds can be at'slightly diflerent levels and only the pipes projecting into a single pond need be brought to exactly the same level. These small localized groups are less sensitive to small changes such as those brought about by settlement of the foundation 1 upon which the structure rests.

- This necessitates a diflerent supply oi the liquid for each pond and the pipes that supply face of the waterstandingin the ponds so the liquid. respectively to the diflerent ponds are designated by 21 in the figures. The water is going to the individual ponds, and a vertical pipe .20 is connected to the end oi each horizontal feeder 21 to carry the water downunder the suras to disturb it as little as possible. The manner in which collecting electrode pipes and 6 are discharge electrodes which may be wires, twisted rods, or other members which the 5 are supported by top header 13 is shown in detail in Figures 4 and 5, in order to bring outclearly the manner in which the top edges of these pipes are brought to the desired level and the fiow of liquid over their surfaces, is made uniform; To pipe 5 is welded an annular angle flange through the horizontal web of which project three or more machine screws 41. This assembly of pipe and flange is held on header plate 13 which is preierablyof sheet metal such as steel plate and which is supported by a framework made up of members 14. The holesin plate 13 are just large enough to permit the belied end as indicated at 5-1) to slip through. The outside diameter of the tubeof flanges 40 is such that they make an easy fit in the holes so when they are inserted as shown they almost fill the holes. Machine screws 41 support the pipe and permit it to be raised or lowered as desired.

Having described the actual arrangement of the precipitator, its assembly will now be described.

Shell 1 is set up and" left plumb in a vertical position. Header plate 13 is placed on the framework consisting of parts 14. The partition plates 26 which divide the header into. troughs or ponds are now welded into place. Pipes 5 with flanges 40 are. next put down through the holes in the header plate and left supported by screws 41. The pipes 5 are next made plumb by using the screws 18 at the bottom of th pipes. The pipes are now leveled with the al of the screws 41, using a straight edge and sensitive level. While an endeavor is made to have the upper or weir edge 5a of all-pipes approximately at the same height, it is only necessary to have the pipes of a single group, that is, the pipes within one trough put at exactly the same level. After this preliminary leveling is made, hot mastic, preferably asphalt and asbestos fibres, is poured in a heated condition around the pipes as shown at d2. After this has cooled somewhat, a layer of soft asphalt, preferably without fibres, is spread over the mastic. This is indicated at 43. While different constructions may demand different 12o thicknesses of the mastic and asphalt, satisfactory results have been obtained with a mastic coating 1" thick and a top asphalt coat of ".in thickness. It is important in every case'to have the top of machine screws 41 above the asphalt 125 so they can be reached and turned with a wrench. The apparatus is now ready for the final leveling of the pipes. Before the pipes are subjected to tests with a liquid, the top edge and inner surface of the pipes are washedwith a solution of 130 caustic soda or other metal cleaner. Liquid is then flowed into a pond or trough by manipulating the valve 22 which corresponds with that trough. Careful inspection of the various pipe tops shows which ones are low or high and screws 135 41 are turned until the proper height is secured. When alltops are at exactly the same height, the same amount of water flows over each one. This can be checked by collecting the water-leav ing the bottom of the pipes. While the procedure just described is often suflicient to get an even distribution of water around the top of the pipes, it may be necessary to file and hand grind parts oi the edge 5-0 oi some oi the pipes. 5-a is a 145 machined edge which has been accurately turned before the pipe is put in position, but so sensi v the is the flow of water to little irregularities in the-height of the pipe top, which constitutes a v weir, that hand filing s i polishing must usua y 1 d tributed' around the top of the pipes.

; uid, during winter months.

he. resortedto before the water is evenly dis- The purpose of the mastic and asphalt is to secure the maintenance of a liquid and gas tight joint between the pipes and top header while the pipes are being leveled and when the prec'ipitator is in operation. The asphalt has sufflcient flexibility to permit the pipes to be raised through the distance required for the final adjustment without having the bond between the asphalt and the pipe broken. And as the asphalt isprotected from deteriorating gases by the water it retains its flexibility and permits realignment of pipes at any time.

-.--Packed,joints and similar connections are not only expensive but usually require servicing fromtime to time if they are to be kept tight to liquids. The construction described makes all such joints unnecessary. After a heavy structure such as anelectrical precipit'ator has been supported by a foundation for a considerable period, the foundation is very apt to settle. Such settlement' may throw "a precipitator oi the type described so far out of alignment that flow over the. various units will become very uneven. With the present arrangement it is very easy to realign the various pipes and again secure an even distribution of liquid.

-;It is possible to provide approximately the same amount of water in each trough by use of valves 22, and if the same number of pipes receive water from each trough the thickness of the film on each pipe will be very nearly equal. However, it is dificult to check this if the precipitator is in operation, especially if the gases being treated are blast'furnace gases, or other gases which must not be diluted with air, which makes it impossible to inspect the apparatus while the gas is passing. .To take care of this situation the water control shown in Figure 6 may be provided. Box is supported horizontally near the top of the precipitatcr.. The purpose of the box is to provide heat and heat insulation to the pipes carrying the washing liq-- Steam supply pipe 51 and steam coil 52 make heating by steam possible. Pipe 23 supplies the liquid to the indi vidual supply pipes 21, which correspond to pipes 21 in Figures 1, 2 and 3. The amount supplied to each pipe is regulated by means oi valve 22, and a three-way valve 53 permits the liquid to go either to the trough through pipe 21 or to atmosphere through pipe as. .iiter valve 22 has been turned to what is considered a proper setting, the amount of water passing can be checked by operating valve 53 by means of handle 55 because with valve 53 all the water can be made to go through pipe 54 into any vessel for collection and measurement.

When dirty water is used for wetting the collecting surfaces, sediment may collect along the-top edge of pipes 5. Also if an endeavor has been made to operate with a minimum amount of water, it is possible that some parts of the collecting surface have not been adequately washed. To provide against these conditions accumulating until trouble results, it has been found advisable to occasionally hood the troughs with an excessive amount of water so that excess goes over the weirs and thoroughly washes the collecting surfaces. In orderthat thisiiush ing may be brought about without disturbing the setting oi valves 22. an auxiliary supply is brought in through pipe 56, which is shown only in Firure 6. When a large amount of water is liberated in pipe 56 by opening valve 5'7, it flows down the .various pipes 58 into pipes 21, which in turn flood the ponds and cause an excessive flow over the top of each pipe 5. In some cases this flushing may be necessary twice a day, but in some installations it has been found necessary only once a week.

Tangential nozzles could be located in the top header and caused tothrow a stream of water into the flared top of pipes 5 which would, in a sense, accomplish the same purpose as the overzles requires considerable additional piping and it is not as desirable a manner of meeting the need for occasional flushing as in the overflow system just described.

Various liquids may be used to wet andwash the surfaces of the collecting electrodes. Water is commonly used and has proved very satisfactory for precipitators used for the secondary cleaning of blast furnace gases. For primary flow just'desoribed. However, this use of nozcleaning of blast furnace gas a liquid with higher vapor pressures than those possessed by water must be used because of the higher temperatures prevailing. Hydrocarbon oils and various other organic liquids can be used for such purposes. Recirculation systems will be advisable when more expensive liquids are usedand filters, or other liquid conditioning means, will be useful in such systems. Wetting agents added to water make it more useful in meeting some problems. Sodium silicate has been successfully used, as described, in copending application Serial No. 584,722. v 1

When high temperature gases are being cleaned, not only must the washing liquid have a high boiling point, but the material of which the flexible seal on the header plate is made must have a high melting point. Asphalt with a high softening point and reinforced with asbestos fibres does very well, but other non-hardening materials can be used. The sealing material must not be dissolved or deteriorated by the wash liquid in contact with it.

Under certain conditions it may be desirable to avoid the use of sealing materials, such asasphalt. Figure 7 shows a construction which makes it unnecessary to use a flexible seal on-the top header. Flange 45 is bolted to header plate lib do with a gasket 47 between to make a liquid tight joint. Cap i8 is held on pipe is with a iric= Another construction which makes it possible I to avoid the use of asphalt or other flexible sealing material is shown in Figs. 8, 9 and 10. Re-' ierring to these figures, it will be seen that the flange ib-a has upon it projecting edges 53 which. are so made that their external diameter is slightlygreater, say {5th of an inch greater, than is-the hole inthe metal header plate 13 in which they are to fit. Two sets or screws are required to adjust this combination. When the pipe. 5 is dropped through. the hole in header plate 13 the ridges 58 will not enter the hole until forced tov do so by screws dlA-b which turn freely in iiange ail-a, but which are threaded into plate 13 By pulling on these screws the flange is forced into the hole in the header plate and the iorced fit thus made is gas and liquid tight. 1!,

however, in pulling-the flanges into the holes, the top edge of pipe is too low, it can be raised by releasing the hold 0! screws 41--b and turning screws 1-&. The latter screws are threaded into the flange, but merely rest upon header plate 13. It is readily seen that by adjusting the two sem of screws the pipe can be brought to any desired height.

We claim: 1. In an electrical precipitator, a horizontal means providing a gas and liquid tight joint between the collecting electrodesand the header,

means for adjusting the level of the upper end of said collecting electrodes, means cooperating with said header to provide a reservoir for washing liquid, members dividing said reservoir into a plurality of pools,. and means for supplying washing liquid to said pools.

2. In an electrical precipitator, a horizontal header, a collectingelectrode projecting through said header, flexible means comprising a thermoplastic sealing material providing a gas and liquid tight joint between the collecting electrode and the header, means for altering the position of the collecting electrode in the header, means cooperating with said header to provide a reservoir for washing liquid, and means for supplying washing liquid to said reservoir.

3. In an electrical precipitator, a horizontal header, a plurality of vertically disposed collecting electrodes projecting through said header,

.a plurality of pools, and means for supplying washing liquid to said pools.

4. An electrical precipitator comprising a plurality of vertically disposed collecting electrodes, a plurality of discharge electrodes spaced therefrom, a horizontallydisposed header through which the upper ends of said collecting electrodes project, means providing a gas and liquid tight joint between the collecting electrodes and the header, means cooperating with the header to provide a reservoir for washing liquid, means for supplying washing liquid to said reservoir, and means for leveling the upper end or each of the collecting electrodes in said header and for adlusting the upper ends of said electrodes to'a common level.

5'. An electrical precipitator comprising a plu-. rality of vertically disposed collecting electrodes, a plurality of discharge electrodes spaced therefrom, a horizontally disposed header through which the upper ends of said collecting electrodes project, means providing a gas and liquid tight joint between the collecting electrodes and the header, means cooperating with the header to provide a reservoir for washing liquid, members dividing said reservoir into a plurality of pools,

means for supplying washing liquid to said pools,

and means for adjusting the upper ends 01. the

collecting electrodes in each of said pools to a common level.

6. In 8?. electrical precipitator, a horizontal header, a plurality of vertically disposed collectmeans for adjusting the level oi the upper end of said collecting electrodes. means cooperating with said header to provide a reservoir for washing liquid, members dividing said reservoir into a plurality of poolsfand conduits for supplying washing liquidto each of said pools.

'7. In an electrical precipitator, a horizontal header, a plurality oi vertically disposed collecting electrodes projecting through said header, means providing a gas and liquid tight joint between the collecting electrodes and the header, means for adjusting the level of the upper end of said collecting electrodes, means cooperating with said header to provide a reservoir for ing liquid, members dividing said reservoir into a plurality of pools, conduits for supplying washing liquid to each of said pools, and flow control means in said conduits.

8. In an electrical precipitator, a horizontal header, a plurality of vertically disposed collecting electrodes projecting through said header, means providing a gas and liquid tight joint hetween the collecting electrodes and the heer, means for adjusting the level of the upper end of said collecting electrodes, means cooperating with said header to provide a reservoir for washing liquid, members dividing said reservoir into a pulurality of pools, conduits for supplying washing liquid to each of said pools, flow control means in said conduits and means for measuring the flow of liquid in said conduits without altering the adjustment of said flow control means.

9. In an electrical precipitator, a horizontal header, a plurality of vertically disposed colleot= ing electrodes projecting through said header, means providing a gas and liquid tight joint lie-=- tween the collecting electrodes and the header means for adjusting the level of the upper end of said collecting electrodes, means cooperating with said header to provide a reservoir for wash-=- ing liquid, members dividing said reservoir into a plurality of pools, conduits for supplying wing liquid to each or said pools, flow control'means in said conduits and means for occassionally supplying an excess of liquid to said pools without altering the adjustment of said flow control means.

10. An electrical precipitator comprising a plurality of vertically disposed collecting electrodes,

a plurality oi discharge electrodes spaced therev from, a horizontally disposed header through which the upper ends of said collecting electrodes project, flexible means comprisinga thermoplastic sealing material providing a gas and liquid tight joint between the collecting electrodes and the header, means cooperating with the header to provide a reservoir for washing liquid-members dividing said reservoir into a plurality of pools, means for supplying washing liquid to said pools. and means for adjusting the upper ends of the collecting electrodes in each oi. said pools to a common level.

11. An electrical precipitator comprising a plurality of vertically disposed collecting electrodes, a plurality of discharge eletrodes spaced therefrom, a horizontally disposed header through which the upper ends of said collecting electrodes project, means providing a gas and liquid tight joint between the collecting electrodes and the header, means cooperating with the header to provide a reservoir for washing liquid, means for supplying washing liquid to said reservoir, and weir members movably positioned on the upper ends of each of said collecting electrodes, said weir members being adjustable angularly to the header, means cooperating with the header to provide a reservoir for washing liquid, means for supplying washing liquid to said reservoir, and adjustable means supporting each of the collecting electrodes whereby the upper ends thereof may be brought to a common level and adjustable positioning means associated with each collecting electrode whereby its upper end may be leveled.

ALEXANDER N. CROWDER.

ROBERT B. HESSON.

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