US1913784A - Resistance in series with electrodes - Google Patents

Description

June 13,1933.

H. A. WINTERMUTE I RESISTANCE IN SERIES WITH ELECTRODES Filed May 18 1927 3 Sheets-Sheet l gwucmtoo fid/w 24.41%

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June 13, 1933. H. A. WiNTERMUTE RESISTANCE IN SERIES WITH ELECTRODE-S Filed May 18, 1927 3 Sheets-Sheet 2 gwwmtoi MM], A MW June 13, 1933- H. A. WINTERMUTE RESISTANCE IN SERIES WITH ELECTRODES Filed May 18, 1927 3 Sheets-Sheet 3 i] A MM @MMW) kmuwt;

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Patented June 13, 193

HARRY A. WINTERMUTE, OF PLAINFIELZD, NEW JERSEY, ASSIGNOR T0 RESEARCH PATENT OFFICE CORPORATION, OF NEW YORK,'1\T. Y.,,A CORPORATION OF NEW YORK RESISTANCE IN SERIES W'ITH ELECTRODES Application filed May 18,

' ,This invention relates to the art of electrical precipitation of materials (such as dust, fumes, etc.) suspended in gases.

The precipitation of such materials is effected by passing the gases containing them through a high-tension electrical field, in which high electrical potential difference is maintained between electrodes, the material being deposited on such electrodes.

' In practice, it has been found desirable to use a number of electrical precipitation units connected in multiple. 3

This practice while it enables large volume of gas to be handled has been found to present certain difliculties in that as more units (each unit consisting of a number of discharge and collecting electrodes) are connected in multiple, the voltage or potential difference between the electrodes of each unit has to be lowered, in order to prevent the increased tendency to are over.

Electrical precipitation systems comprise in general a step-up transformer, a rectifier to change the alternating current to a pulsating direct current which is delivered to the discharge electrodes of the precipitator, through which the gases carrying suspended material are passing. In this high tension circuit surges, oscillations or tran-.

sient currents may be set up and kept in existence by the pulsations from the rectifier feed, the changing of the gas conditions, the static charge in the precipitate, variations in current flow from the corona discharge points, etc., etc. The precipitator itself has considerable inductance and capacity, which are distributed and tend to foster and aggravate this surging condition.

The larger the units or the more units in parallel, the more pronounced this tendency to surging or oscillation is found to be. Such oscillations may take place between units or different parts of the same units and while they may be of small power value, are often just large enough when superimposed on the main voltage, to cause disruptive discharges at points where they happen to reach a maximum value.

Furthermore, when such disruptive discharge or arcing occurs, or when for any m7. Serial No. 192,376.

other reason a relatively large flow of current occurs at a certain point or portion of the precipitator, the voltage is immediately reduced in the remainder of the precipitator, due to the flow of energy from such other portion through the relatively low resistance path at this point. This phenomenon, which maybe called localization of the electrical field, not only results in a waste of electrical power, but-decreases the efficiency of the precipitating action which is dependent upon the maintenance of a high potential difference between all portions of the opposing electrodes.

When such conditions exist or arise, it is necessary to reduce the precipitating voltage in order to prevent such breakdowns, which reduces the corona discharge, and lowers the percentage of recovery.

It is characteristic of electrical precipitators comprising separated electrodes between which a stream of gas is flowing that a small increase of voltage above a given discharge point very greatly increases the current flow (corona discharge) thereby increasing the efliciency of the precipitator. In other words, the gas resistance does not remain constant, but decreases with increased current flow.

In the usual treater the current flow may be largely localized in a relatively few points in the treater leavin the remainder of the unit practically ined ective. By the use of resistances or impedances so distributed as to break up the treater or unit into relatively small parts isolated from each other by such resistances or impedances and with resistances or impedances also located in the direct path of the current flow, any tendency to localization due to whatever cause produces a potential drop in its path partly neutralizing the tendency towards localization and at the same time the adjoining elements are prevented from pouring their energy into the disturbed area by l the separating resistance or impedance.

Surges, high frequency oscillations, etc., are primarily generated at the rectifier and transmitted to theactive treater parts. The connecting lines, insulators, bushings, etc.,

and active parts of the treater including the gas, deposits on the collecting electrodes, etc, all compose a complex electrical circuit which is capable of reflecting 'the surge waves received from the rectifier and so producing standing voltage waves within the treater. Such stationary waves occurring in the active treater produce localized current flow. The resistances or impedances introduced in the circuit betweenthe active treater parts and the rectifier tend to prevent the establishment of such standing waves and thus produce uniform-distribution of current flow throughout all parts of the treater and so maintain every part at maximum efiiciency at all times.

The snapping which ordinarily occurs without producing power arcs is probably due to the breakdown of these standing Waves, the energy discharged at the time of rupture or in a single snap being only the energy of the particular wave discharged. However, the discharge of one such wave produces disturbances in adjoining or neighboring waves causing them to break while the original wave is developing its original potential. In this manner continual snapping in the treater is developed and the voltage in the treater can only be further increased at the expense of a further increase in the rate of snapping with enor-' mous increase of current flow, most of which current is undoubtedly used in the snapping or in the maintenance of the standing waves.

It is well-known that a small treater, say a single pipe or plate, is far more eliicient than the results per pipe or plate obtained from a group of similar units in multiple.

The use of suitable values of resistances or,

impedances in series with both sides of the circuit to each unit (including its discharge electrode).p'roduces a condition of isolation equivalent in some degree to the operation of the units singly.

Therefore this invention has for its main object to provide means whereby an increased voltage and the accompanying increased efficiency may be uniformly and continually maintained at each of a number of interconnected electrical precipitation units or elements. A further object of the invention is to prevent or minimize arcing or disruptive discharge, and to also minimize localization of the electrical field at certain portions of the precipitator.

These results are attained by subdividing the precipitator system into as small elements as possible and placing suitable impedances such as resistances, between these elements, by which oscillations and localization of the electrical field are practically eliminated.

As each element is small, the amplitudes of the oscillations are smaller than they would be if they were all in parallel with no preventive means between them. Such oscillations as may tend to arise are promptly damped or dissipated and preventedfrom reaching harmful values. Furthermore, a mon'ientary increase in current flow through any element due to any disruptive discharge which might occur or to any other cause would in turn produce such a drop in potential across the resistance in series with such element as to. immediately lower the potential difference between the active portions of such elementsuiiiciently to immediately suppress such increased current flow without appreciably lowering the voltage in other portions of the precipitator.

By thus distributing impedances,etc., in the high tension circuits, the corona discharge at any element is made substantially independent of that from any other, thus enabling more complete and accurate control of the system. i

This fundamental idea of providing sufiicient impedances between adjoining corona discharges can be applied not only between the units of an electrical precipitation system, but to other localities in the system. in which like conditions of oscillation and localization are liable to occur, and even to the individual discharge electrodes, and examples of such application of the broad invention are described later.

As has before been pointed out, it is a characteristic of electrical precipitators that a relatively small increase in voltage may produce a relatively very high increase in corona discharge. As the suspended particles in their passage through the precipitator between the discharge and collecting electrodes are subjected to a greater number of corona discharges, a more efiicient separation is eliected.

As the resistance of a precipitator does not remain constant but decreases with increased current flow, it is said to have negative resistance characteristics, and as the flow is increased the operation becomes more unsteady, resulting in arc overs or highly localized" discharges. In some precipitation problems, unless gas conditioning is used, conditions are met in which It is in these cases that ballasting impedances in series with each corona point are most effective, giving stable current flow and preventing the localization of discharges in a relatively few points. The voltage throughout the precipitator is maintained at the normal value resulting in an ever. distribution of corona discharge, thus maintaining a maximum efiiciency. As resistances there may be used wirewound resistances, carborundum rods, or resistances of the semi-conducting type, such as Portland cement concrete, Transite board or the like. The resistance, through" moisture or precipitate or both, on the surface of insulators or semi-conducting material, may also be utilized.

As a further development of this invention, the use of these resistances of the semi-conducting type permits the insertion of resistances in close connection with the discharge electrode supports or collecting electrode supports, or even with the discharge elements of each electrode.

The apparatus used mayl take a great variety of forms, some of w ich are illustrated in the accompanying drawings from which the invention will be readily understood.

Referring to the drawings:

Fig. 1 is a diagram of a system illustrate ing an embodiment of the invention;

Figs. 2, 3 and 4 are front elevations of supporting devices for the series of discharge electrodes;

Figs. 2a, 3a and 4a are corresponding end views;

Figs. 5, 5a, 6 and 6a are elevations and plans of modified forms of discharge electrodes;

Fig. 7 is a horizontal section through a modified form of precipitator.

Referring to Fig. 1, P, P are precipitators having discharge electrodes 2, 2 and collecting electrodes 3, 3 the discharge electrode being tensioned by weights W, as is usual. T is a transformer by which the voltage is stepped up to the required degree, The ends of the secondary coil are connected through choke coils PC (here indicated as of the pancake type) to two terminals of the rectifier whose other two terminals tween this beam and the electrode carrying pipes F, F is interposed a block 0 of highresistance or semi-conducting materialsuch as Transite or concrete. The high ten,- sion connections to the pipes F, F, may be made throu h additional external impedances R, or t ese external resistances may be omitted, and the high tension line B connected to the supporting beam D, as shown. In this case the resistance of block 0 is interposed in the circuit of each set of discharge electrode members.

In Figs. 3 and 3a a pair of conducting the conducting support and each discharge electrode.

In Figs. 4 and 4a is shown a modified form in which blocks 7, 7 of hi h resistance material are carried by con ucting supports from the pipes F, the, discharge electrodes 5, 5 belng supported from these blocks.

A still further extension of this invention is possible. In the ordinary form of continuous conducting discharge electrodes, the points at which the corona discharge occurs are haphazardly distributed over the electrode. By providing definite discharge points, it becomes feasible to insert ballasting resistances directly at each discharge point or'group of points.

Thus Figs. 5 and 5a show a discharge electrode comprising a central conductor 10, on which are arranged hollow blocks 11, having' projecting arms 12 provided with points 13 made of metal or of the block material. The blocks and arms are made of high resistance material, thus interposing re ulated resistances between the central con uctor and the discharge points.

A modified arrangement is shown in Figs. 6 and 6a. In this case a flat block 14 of high resistance material is provided at its edges with'one or more discharge points 15, 15 and supported by a conducting support as a chain 16. While the points 15 are very desirable, their use is not necessary, and satisfactory distribution of corona points can be secured without the aid of these.

In each of these last two cases, the discharge electrodes are preferably arranged with their longer dimension parallel to the flow of the gas and between the parallel collecting electrodes, as shown in Fig. 7, in which the discharge elements, such as those shown in Fig. 6 are shown arranged between parallel collecting electrodes 20, which may be either vertically arranged metal plates or blocks of semi-conducting material such as concrete.

Some of the advantages of the point construction of discharge electrodes are that alternating current may be used, or the points may be either negatively or positively charged. Moreover, if arcing occurs at any point, this arcing would not affect the corona discharge at the other points, as is the case when there is no high resistance.

It will thus be noted that the parallel circuits as heretofore used in electrical precipitation systems are broken up by resistances, whether these parallel connected elements are precipitator units, sections of units,

smaller groups of discharge electrodes, single discharge electrodes, smaller groups of collecting electrodes, single collecting electrodes or discharge points on a discharge electrode.

, The improved result in general is that it becomes possible to maintain a current discharge from discharge to collecting electrodes which is substantially free from currents of an oscillatory or high frequency nature,

This uniformity or evenness of current discharge per unit length of electrode permits theuse of higher voltages than can now be safely used in any of these interconnecte electrical precipitator systems.

The amount of ballasting resistance or other impedance to be used in series with any unit, section, or electrode, can.not be definitely stated in ohms, since the amount used depends upon a number of factors, among which are the spacing distance between discharge and collecting electrodes, the kind of gas and the particular character of suspended precipitate, the length of the electrodes, etc. Further many types of high tension resistance do not have the same amount of resistance in pulsating rectified currents as they have on high-voltage direct currents. I

However, according to this invention the resistance or impedances in series between any two precipitator units, sections, electrodes or points must, under all ordinary conditions be suflicicnt to prevent the localization of discharges or the cross surges or oscillation between the adjacent elements and, for convenience, resistance or impedances of this order are termed surge-resistance impedances or resistances.

It has been the custom to insert resistances in the high tension circuits, as for example at the shoes of the rectifier, but these resistances were small, usually varying from 1000 to 10,000 ohms, While according to this invention resistances of 100,000 ohms or more are inserted in each of the paralleled leads from the high-tension line to the precipitators.

It has also been the practice when precipitator units were to be operated in parallel, to introduce resistance on the low voltage side of the transformer. With large size units and a large current flow the use of resistances in the low tension circuit must be minimized to avoid excessive power losses, and where a short circuit occurs in the precipitator an excessive rush of current can happen because of the small amount of resistance in the high-tension circuit.

When the high resistances are distributed in the manner described, these difiiculties are largely obviated.

lhe term element as used in the claims is intended to include a section or unit of an electrical precipitator, a set of electrodes in necting said discharge electrodes in parallel to a high-potential source, said means including semi-conductive material interposed between each discharge electrode and the high-potential source.

2. In a system for the electrical precipitation of suspended particles from gases a supporting structure, a supporting mem er of semi-conducting material mounted on said supporting structure, a plurality of discharge electrode aneans mounted on said semi-conducting supporting member and connected thereby to said supporting structure, a source of high potential electrical current, and means electrically connecting said supporting structure to one side of said current source.

3. In a system for theelectrical precipitation of suspended particles from gases comprising a plurality of. discharge electrodes, a conductive supporting member therefor and a semi-conductive material interposed between said supporting member and said electrodes.

4:. In a system for the electrical precipitation of suspended particles from gases comprising a plurality of discharge electrodes, a con uctive supporting member therefor and a semi-conductive member interposed between said supporting member and said electrodes, said semi-conductive member serving also to separate said electrodes from each'other.

5. ln an electrical precipitator, a discharge electrode system comprising a plurality of discharge electrode elements, semiconductive material separating each electrode element from the other electrode elements, and a conducting member for supplying current to each of said electrode elements through said semi-conductix e material.

6. A discharge electrode element comprising a conductive supporting member, a plurality of spaced conductive discharge points, and semi-conductive material between each of said discharge points and said conductive member.

7. A system for the electrical precipitation of suspended particles from gases comprising collecting electrodes defining a plurality of gas passages, discharge electrodes opposed to said collecting electrodes for creating electric fields within said passa es, a source of high voltage current, para lel connections between said current source and the discharge electrodes in the separate gasv passages, and semi-conductive material in the connection to each of said discharge electrodes.

In testimony whereof, I aflix my signature.

' HARRY A. WIN TERMUTEL

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