US1903644A - Concentrated field precipitator - Google Patents

Description

April 111, 1933. A F MES-TON L9$fi44 I CONCENTRATED FIELD PRECIPITATOR Filed Jan. 4, 1952 3 Sheets-Sheet l Aprifi 11 1933. A. F. MESTON L W CONCENTRATED FIELD PRECIPITATOR Filed Jan. 4, 1952 3 Sheets-Sheet 2 April 11, 1933. A F MESTON 1,903,644

CONCENTRATED FIELD PRECIPITATOR Filed Janf4, 1952 3 Sheets-Sheet 5 III Patented Apr. 11, 1933 UNITED STATES PATENT OFFICEv A RGHIIBALD I. MESTON, F MIDDLESEX, NEW JERSEY, ASSIGNOR TO RESEARCH 30 PORATION, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK GONCENTBATED FIELD PRECIPITATOB Application filed January 4, 1932. Serial No. 584,684.

' erally useful in increasing the efliciency of operation, is particularly useful as applied to the treatment of ases which tend to give rise to excessive spar -over or disruptive discharge between the electrodes of the apparatus. Y

The treatment of some gases by electrical precipitation has raised problems that have been quite difiicult to solve. Certain of the difficulties are evident as soon as traces of the suspended matter are removed from the'gases and deposited on the collecting electrode surfaces. For example, the cleaning of blast furnace gases over a rather wide temperature range has proven troublesome because of the characteristic of the deposited dust to cause disruptive spark-overs between the electrodes. Lowering the voltage until spark-over does not take place reduces the efiiciency of the precipitator to such an extent that its operation is uneconomical. Spraying water into the gases is beneficial, but results in the loss of desirable sensible heat, or the raising of the humidity of the gases, or both. Flushing the collecting electrodes is also possible, but is objected to for the above and other reasons. Rapping and scraping has been attempted, but it is extremely diflicult to maintain the total surface of the collecting electrodes sufficiently clean to overcome the spark-over condition set up by such dusts as those in raw blast furnace gases.

In accordance with the present invention, the electrode systems are so arranged and the potentials employed are such that a highly concentrated field is established to only a minor portion of the collecting electrode surface. and this portion of the collecting electrode is continuously or substantially continuously cleaned to prevent spark-over.

At both sides of this highly concentrated field, the field is of sufficient strength to force the charged particles to the collecting electrodes, but is too weak to result in sparkover even after considerable dust of a refractory nature has been deposited. The major of such a nature that it will fall by gravity before it builds up to an objectionable degree.

One of the objects of the present invention is to provide electrical precipitation methods of and apparatus for the treatment of gases,

such as hot blast furnace gases. A more general object is to provide improved methods of and apparatus for the-removal of particles suspended or entrained in a body of gas.-

further object is to provide electrical precipitation methods and apparatus that are characterized by the joint use of electrical fields of high and low concentration, and the thorough and continuous or nearly continuous cleaning of the portions of the co1- lecting electrodes at which the highly concentrated fields terminate. 7

These and other objects of the invention will be apparent from the following specification, when taken with the accompanying drawings, in which:

Fig. 1 is a fragmentary plan view, with parts in section, of one embodiment of the invention;

Figs. 2 and 3 are fragmentary side and end elevations, on lines 2-2 and 33, respectively;

Fig. 4 is an enlarged elevation in partial.

sections illustrating other forms of and methods of cleaning the auxiliary electrode surfaces; and

Figs. 11 and 12 are plan views of other types of precipitators embodying the invention.

In Figs. 1 to 5, which illustrate a horizontal flow plate type of precipitator, the numeral 1 identifies the casing through which the gas moves in a plurality of parallel passages that are provided by the collecting electrode system. The side walls of easing 1 may be, and preferably are, employed as the major portions of the outer collecting-electrodes, and the corresponding portions of the intermediate collecting electrodes are provided by steel plates 2 whose upper ed es are secured to the top wall of casing 1. he plates 2 of each electrode are spaced apart to clear the ipes or rods 3 that are of substantially arger diameter than the thickness of the plates 2, and therefore project into the gas passages to constitute the terminals of the highly concentrated electric field. Half-round bars or pipes 3 are similarly arranged adjacent the side walls of the casing. For convenience of description the pipes 3, 3 will be referred to as auxiliary collecting electrodes or surfaces, while the plates 2 and side walls of the casing will be designated as the main collecting electrodes or surfaces.

The upper ends of the auxiliary collecting electrodes slide in glands 4 and carry enlar ed heads or anvil tops 5 at their outer en s, with springs 6 arranged between the glands and heads to yieldingly hold the auxiliary electrodes in raised position. The lower ends of electrodes 3 are flattened and have secured thereto the channels or slotted pipes 7 into which the lower edges of plates 2 extend. Where pipes are used as the auxiliary electrodes, the upper portion of each electrode preferably takes the form of a bar 9 having a round section at the top where it is slidable in the supporting gland 4, a round section at the bottom where it enters and is welded to pipe 3, and a flattened section between the ends. When the auxiliary elements are of rod form, each element mav consist of a unitary bar or rod having the same general shape as the composite pipe-bar electrode.

The auxiliary collecting surfaces may be made of metals and other good conductors of electricity, such as are ordinarily used for collecting surfaces. In some cases, howeve'r, it is advantageous to make the auxiliary collecting electrodes of transite, concrete or other semi-conducting material.

The discharge electrodes are of filamentary form, comprising wires 10.which are supported by a high tension framework 11 that is mounted on insulators 12. The framework includes rectangular frame located centrally of each gas passage the wires 10 being attached to the upper bar or pipe 30 of the frame and passed through the lower bar to receive weights 13 that hold the wires taut. As shown in Figs. 1 and 2, the discharge electrode wires are positioned directly opposite and parallel to the several auxiliary collecting electrodes 3, 3'. Since the discharge distance between the discharge electrodes 10 and the auxiliary collecting electrodes 3, 3 is shorter than that to the main collecting electrodes, it will be evident that much of the electrical field will terminate upon the auxiliary collecting electrodes and will set up conditions that will determine the maximum of the voltage to be impressed between the electrode systems.

It will be noted that the flattened rtions nding bars 9 of the auxiliary collecting electrodes 3, 3' are located opposite the u per pipes or bars 30 of the high tension amework 11, thus avoiding danger of breakdown at these points.

A rapping system is provided for the auxiliary collecting electrodes and may comprise ocker shafts 14 mounted on the top wall of casing 1 and carrying hammers 15 for striking the anvil tops 5. The shafts 14 are operated from a motor, not shown, to effect a substantially continuous rapping of the several auxiliary collecting electrodes.

According to the prior practice, such a disposition of the opposed electrode systems which would result in local concentration of the field, has been generally conceded to be undesirable, since the sensitive electrical conditions so established will result in sparkover as soon as material deposits on the auxiliary collecting electrodes to any appreciable extent. The possibility of spark-over may be reduced by decreasing the operating potential, but this results in a loss in elliciency or the damage resulting from sparkover may be reduced by the use of high resistance materials. Neither of these expedients has proved entirely satisfactory, and it has therefore been the usual practice toemploy arrangements which provide for an approximately uniform electrical field throughout the gas passages.

According to the present invention, no attempt is made to avoid the critical electrical conditions resulting from the establishment of the highly concentrated electrical fields. On the contrary, the potential differences between the electrode systems is preferably maintained quite close to that value at which spark-over will occur when the auxiliary collecting surfaces are free from deposited material. An intense field that promotes the liberation of free electric charges, indicated by the vivid corona immediately surrounding the discharge electrodes, exists across the relatively narrow space between the auxiliary collecting electrodes and the discharge electrodes, and while comparatively weak, the electric field between the discharge electrodes and the main collecting electrode surface is sufliciently strong to force the particles, to which the charges have become attached, to the more distant portions of the collecting electrodes. In fact, it has been demonstrated that a substantial portion of powdered coal dust entrained in an air stream will be forced back against the air current and deposited on the collecting electrodes in advance of the first auxiliary electrode surfaces, i. e., on a portion of the collecting electrode surface where the adjacent field is comparatively weak. The deposition on the main collecting electrode surfaces has been found to be quite general, however, bringing out the pertinent fact that the deposition of particles by. a relatively weak field is entirely practical when the particles are first highly char ed by passing through or in the vicinity o a highly concentrated electrical field where many free charges are present.

Since the apparatus is to be operated at voltages just under that conducive to spark-over between the auxiliary electrodes and the discharge electrodes, it will be apparent that it is extremely important that the field conditions be maintained without change between these systems of electrodes. Satisfactory operating conditions can be maintained by a thorough and continuous or substantially continuous cleaning of only the auxiliary collecting electrodes, because there is no danger that spark-overs to the main collecting electrodes will ever take ,place if they are kept reasonably free from projecting deposits. The substantially continuous cleaning of the auxiliary electrodes 3 and 3', which is effected by the continuous operation of the rocker shafts 14, will be sufficient to prevent harmful deposits from building upon these surfaces in the treatment of many types of gas.

In many instances, the minor vibration which results from the continuous rapping of the auxiliary electrode surfaces will be sufficient to dislodge the material deposited on the main collecting surfaces. When required, the main electrode surfaces may be rapped at more or less infrequent intervals, according to present practice of rapping the entire collecting electrode surface, by any appropriate rapping system.

In Figs. 1-3 such a separate rapping means for the main electrode systems is shown by way of example. This rapping means is similar in operation to that used for the auxiliary e ectrodes, but it is arranged to operate less frequently than the auxiliary electrode rapping system. In the figures the main electrode rapping system comprises rocker shafts 31 mounted on the top wall of casing 1 and carrying hammers 32 for striking the anvil plates 33. The shafts 31 are operated from a motor (not shown) to efi'ect an occasional rapping of the main collecting electrodes.

In place of rapping, the auxiliary electrode surfaces may be cleaned by rotating the cylindrical elements 3 about their vertical axes for contact with spring pressed scrapers 16 (Fig. 6) or brushes 17 (Fig. 7) that are mounted at the adjacent edges of the collecting electrode plates 2.

In some instances, the gases and/or the entrained material may be of such a nature that the desired critical electrical conditions which are required for most eflicient precipitation cannot be satisfactorily maintained when the cleaning of the auxiliary electrode surfaces is effected by rapping or brushing. In such cases, the requisite continuous and thorough cleaning of the surfaces may be effected by flushing with wash liquids. As shown in Fig. 8, the auxiliary collecting electrodes may comprise pipes 3 which are suspended by the spacers 18 from low pressure supply pipes 19 that deliver a slow stream of water or flushing liquid to the interior of the electrode. The wash liquid spills over the open top of the pipe 3 and forms a film that moves down the exterior of the pipe to carry off the deposited material before harmful deposits are formed.

This embodiment of the invention is particularly useful in the treatment of hot gases when it is desired to conserve the heat content of the gases. Since the auxiliary electrodes constitute but a minor part of the total collecting electrode surface, the contact of the gases with the flushing 1i uid effects only a relatively small reduction 1n the temperature of the gases, and does not materially increase their humidity. It has the further advantage that the water and collected solids may be directed into the main collecting hoppers where it will be mixed, say by a screw conveyor, with the dry dust collected on the main surfaces to produce a readily transportable material which will not form dust clouds in handling, but which will be comparatively dry.

The auxiliary collecting electrode surfaces may be formed in various ways and other examples are shown in Figs. 9 and 10. As

shown in Fig. 10, the surfaces which project beyond the main collecting surfaces or plates 2 may be provided by a pair of connected plates 20 which lie at opposite sides of plates 2 and have semi-circular central portions and end flanges which overlie but are spaced from the edges of pates 2. In the form shown in Fig. 9, the main collecting electrode may be a substantially continuous plate formed by connecting plates 2 by clamps 21, and the auxiliary collecting electrodes take the form of bulging plates 22 that overlie the clamping strips 21. It is to be understood that these auxi iary collecting electrodes are so supported that they may be continuously or substantially continuously cleaned while the main collecting surfaces are cleaned but intermittently, if at all.

The invention is not restricted to the plate type of precipitator, but may be applied to various other forms. the main collecting e ectrodes 23 may take the form of corrugated plates so arranged that the gas passages vary in cross-section throughout their length. The discharge electrodes 24 extend through the regions of greatest transverse width and auxilary collecting electrodes 25 extend parallel to the discharge As shown in Fig. 11, 1

5 results in a concentrated field terminating at the auxiliary electrodes.

As applied to the pipe type of precipitator, Fig. 12, a somewhat similar arrangement of auxiliary collecting electrodes 26 between the central discharge electrode 27 and the pipe 28 is employed.

Thorough and substantially continuous cleaning of these auxiliary electrode surfaces permits the use of more intense electric fields, and hence higher efiiciency, than has been possible in precipitators in which the entire collecting electrode surface was cleaned intermittently.

While the invention is particularly directed towards maintaining the collecting electrode surfaces where the electric fields are concentrated in unaltered condition, it is important that no appreciable change take place at the surfaces of the discharge electrodes. As those familiar with the art know, deposits on the discharge electrodes lower the efficiency of the precipitator and, in those problems where some of the suspended material tends to become attached to the discharge electrodes, means may be installed for removing such material before it can appreciably alter the characteristics of the electrodes. Such means are well known to the art; for instance, the discharge electrode rapper shown in Patent 1,813,306 could be adapted to the precipitators constructed in accordance with the invention.

I claim:

1. A method of operating an electrical precipitator of the type having discharge and collecting electrode systems which comprises establishing successive fields of high and low concentration and maintaining the field of high concentration in substantially a uniform condition.

2. A method of operating an electrical precipitator of the type having discharge and collecting electrode systems which comprises establishing successive fields of high and low concentration and maintaining the field of high concentration in substantially a uniform condition by keeping the terminals of the field of high concentration substantially free of deposited material.

3. A method of operating an electrical precipitator of the type having discharge and collecting electrode systems which comprises establishing successive fields of high and low concentration and maintaining the field of high concentration in substantially a uniform condition by substantially continuously cleaning the collecting electrode terminals of the concentrated field.

4. In the operation of an electrical precipitator of the type having discharge and collecting electrode comprises establis ing a relatively narrow electric field of high concentration and relatively wide and comparatively weak fields at each side of said concentrated field, maintaining the potential between said electrode s stems at a value approaching that at which spark-over will occur when the collectin electrode terminals of the concentrated fiel is free from deposited material, and substantially continuously cleaning the collectin electrode terminal of the concentrated fiel 5. In the operation of an electrical precipitator of the type having discharge and collecting electro e systems the process which comprises establishing a relatively narrow electric field of high concentration and relatively wide and comparatively weak fields at each side of said concentrated fields, maintaining the potential between said electrode systems at a value approaching that at which spark-over will occur when the collectin electrode terminals of the concentrated field is free from deposited material, substantially continuously cleaning the collecting electrode terminal of the concentrated field, and subjecting the remaining portions of said collecting electrode systems to a lesser degree of cleaning.

6. In the operation of an electrical precipitator having discharge and collecting electrode systems, the process which comprises establishing alternating regions of highly concentrated and relatively weak electrical fields, establishing a potential difference between said systems of an order approaching the production of spark-over in the concentrated field regions, substantially continuously cleaning the portions of the collecting electrode system at which said concentrated fields terminate, and subjecting the remaining portions of said collecting electrode system to a lesser degree of cleaning.

7. An electrical precipitator comprising main collecting electrodes, auxiliary collecting electrodes and discharge electrodes, positioned to establish concentrated fields terminating on said auxiliary electrodes and weaker fields terminating on said main collecting electrodes, and means for maintaining said auxiliary collecting electrodes substantially free from deposited material.

sg'stems the process which" 8. An electrical precipitator comprising aeoaeee collecting electrodes to establish concentratfi fields terminating on said aumdiary electrodes and weaker fields terminating on said main collecting electrodes, of means for cleaning said auxiliary collecting electrodes more thoroughly than said main collecting electrodes.

10. In an electrical precipitator, the combination with main collecting electrodes, auxiliary collecting electrodes, and discharge electrodes positioned opposite said auxiliary collecting electrodes to establish concentrat ed electrical fields terminating on said aum7liary electrodes and weaker fields terminating on said main collecting electrodes, of means for substantially continuously cleaning said auxiliary collecting electrodes and means for intermittently cleaning said main collecting electrodes.

In testimony whereof, I afix my signature.

ARCHIBALD F. WSTON.

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