US1178430A - Process of electrical separation. - Google Patents

Description

H. A. WENTWORVTH.

PROCESS OF ELECTRICAL SEPARATION.

APPLLCATION FILED mac. 2|, I907.

WT EEEE UED STATES PATENT OFFICE HENRY AZOR WENTWORTH, OF LYNN, MASSACHUSETTS, ASSIGNOR'TO HUFF ELECTRO- STATIC SEPARATOR COMPANY, OF IBQSTON, MASSACHUSETTS, A CORPORATION OF MAINE.

To all whom may concern:

Be it known that 1, Hanna: Azon WENT-- WORTH, a citizenof the United"'*States, and resident of Lynn, in the county of Essex and tion of the ingredients ofmixtures of solid comminuted matter, whereof the particles are differentiated as to their electrical conductivity, and consists in an improved method by which the separation of one class of particles from particles of another class may be accomplished.

In the patent granted to me July 16, 1907 No. 859,998, there is set forth and described a method of electrical separation wherein the deposition on and retention by certain particles of a mass under treatment, of localized charges conveyed thereto by an ionized jet, performs a distinctly @1SBfI1l function in efi'ecting the separation of one class of particles from another. "The conditions described in the said patent are such that the stress of the electrostatic field is sufiiciently powerful tocause a repulsion of the more highly conductive particles of the mass from the surface of the electrode on which they rest, in spite of the opposed tendency due to the ionized gaseous jet; the retention of particles of lower conductivity and the repulsion of particles ofhigher conductivity are nearly coincident in both place and time. The relative conductivity of mixed particles may be due to high surface conductivity, or'

to conductivity through the body of the particle, or both.

My inventlon herein described is, at least in the preferred mode of operation, characterized by the production of electrical conditions under which within a portion of the electrostatic field the repellent effect due to electrostatic stressis, with respect to conductive material, counteracted or controlled by an opposed electrical efl'ortdue to the maintenance of a spray or jet discharge from one electrode to another, whereas 1n another portion of the field the qualification of the effect of electrostatic stress by spraydischarge is suspended or eliminated leaving the electrostatic repellent efl'ort free to disengage conductive particles from the sur- Specification of Letters Patent.

PROCESS OF ELECTRICAL SEPARATION.

Patented A r. 4,1916.

Application filed December 21, 1907. Serial No. 407,566.

face of the electrode in contact with which they rest. By the maintenance of such condlt ons as these, I have been enabled to make sat sfactory separations by virtue of differentlatlons in conductivity with an electrostatic field of moderate. potential .as contrasted with the field employed in-many instances in the operation of the process descrlbed mathe Wynne Patent No. 805,694, dated November 20, 1905, and moreover, I have produced good separation under the conditlons named as characteristic of this invention, with substantially continuous potential.

The method which I have invented is properly described as a specific mode of the more broadly claimed process described in the Blake and Morscher Patent, No.

668,791, wherein the patentees state their object to be, in part at least, to charge all particles of a mixture with electricity of one sign, and thenv bring these into contact with an electrode surface, charged with electricity of the opposite sign, and establishing a static field in opposition to another electrode, then to repel the conductive par.-

ticles, while the non-conductors (relatively speaking) are not repelled. By this preliminary treatment all the particles are similarly charged, and thus the time required for an inferior conductor to lose this charge and acquire that imparted by the active,'or repelling, electrode, is increased over -what would be the time required were all the particles in neutral condition when applied to the repelling electrode. My method involves also the application to all particles of a mixture of a charge opposite in sign to the charge .of a subsequently operative repelling electrode surface, and, later the subjection of the pre-charged mixture to the repelling acti'on due to a charged electrode in a field of substantially pure static stress, the said field being produced by the presence of a statically charged electrode opposite to the material-carrying electrode, as in the Blake and Morscher patent; the difierence however being principally in the mode with which I administer the preliminary charge, and secondarily in the mode with which I apply static charge to the surface of an electrode opposite to that of the material carrying electrode. 7

Inthe drawings hereto annexed which illu'strate diagrammatically an apparatus suited to the performance of my method,- Figure 1 is a view, partly in perspective, of the elementary members of such an apparatus; Fig. 2 is across sectional view diagrammatically illustrating the electrical conditions which exist in the performance of my method; and Fig. 3 shows an apparatus, in perspective, with portions of a suitable frame and accessories.

Referring to the drawings, E is a material-receiving electrode which is preferably a cylinder with a good conducting surface mounted to rotate upon its axis in the direction indicated by the arrow.

H represents a hopper or equivalent apparatus for feeding the material M in a properly distributed stream to the surface of electrode E. The opposed electrode E" is shown as a fine wire stretched parallel to the surface of the electrode E to the axis thereof. The proportions of the electrode E are therefore such that when the two electrodes E E are connected respectively to the termmals of a suitable generator (not shown) the electrostatic field between the two electrodes is qualified and modified by the formation of a silent spray discharge proceeding from the electrode E. Other forms of spray discharging electrodes are well known; a knife edge, or a comb with sharp points may be efi'ectively employed;

This spray discharge is convective and consists probably of particles of air electrified by contact with the electrode E and in part also of electrical corpuscles or, as they arenowadays termed, ions which shoot across from one electrode to the other. Probably, also, the air particles or molecules travel from one electrode to the Other at a much lower rate thanthe disengaged ions; whatever may be the correct scientific explana tion or analysis of the phenomenon, it is sufficiently well known qualitatively as a spray discharge. The efiect of a spray discharge is that of a leakage involving a transfer from the electrode E to the electrode E of a' portion of its electrical charge and this spray modifies the rate of drop in potential from point to point between the electrodes and distributes the drop in potential in varying rates in the regionalfecteol. When the particles of mixed material M are carried into this field they are sprayed by the spray discharge and receive electric charges similar in sign to that of the electrode E and retain these charges with a persistence which is, roughly speaking, inversely in proportion to the rate of surface leakage Or other leak- 1 age such as bodily conduction through the particles themselves; these charges and the particles which carry them are attracted to the electrode E. At the same time the electrostatic charge on the electrode E exerts its repellent effort which is responded to by the particles with promptness and emphasis itself; but the instant that such a metallic meaeeo which are, roughly speaking, in proportion to their-electro-conductivity. Thus, all the particles in contact with the electrode E are in a region of conflict between two opposed energetic efforts and their behavior under this condition depends upon the varying degrees of their respective conductivities. In the case of good insulators whereon the surface 01' other leakage is very slow, the deposition of electric charge like in sign to that on the electrode E, causes such particles to adhere closely to the electrode E in the manner described in my Patent No. 859,998 aforesaid. In the case of a particle of good conductive material, as, for instance, a particle of metal, the charge transferred by the spray is quickly conveyed to and neutralized by the opposite charge of the electrode E and the repellent efiort manifests particle leaves the electrode and is free from its contact influence, the spray recharges the particle which, under the new condition, is surrounded by air and is not in actual contact with the electrode E and consequently the particle is thrust back into contact with the electrode E there to lose its recently acquired charge and go through the same operation again. This behavior of metallic particles under the complex conditions of electrostatic stress, contact with a metallic electrode such as E, and spray discharge from the opposite electrode, is admirably demonstrated by observing the contact of fine particles of copper conveyed through the field qualified by spray discharge, Though the potential difference between the electrodes may be so moderate, that the copper particles do not actually leave the electrode with which they are in contact, they demonstrate the persistent repellent efiort by squirming and hopping on the surface; the whose mass of copper particles seems alive. In the case of particles of distinctly the conductive character of the particles employed, and as the conductivity diminishes in degree, the activity of the particles themselves becomes less and less manifest to the eye of the observer; thev repelling charge, orpotential, of the surface remaining the same.

As the spray discharge is continuous or substantially so, the effect on the particles in the spray-affected region-is to give each particle, whether a good or a poor conductor, a persistent charge opposite in sign to the charge on the electrode E.

In the apparatus shown in the drawings ll first pass the mixed material M through that portion of the electrostatic field which L53 the better conductors which repeatedly manifest the repellingtendency but are as repeatedly restrained, are held either in contact with or in close proximity to the same electrode surface. I then convey the mass of material out of the spray-affected region, and preferably into a portion of the electrostatic field which, relatively speaking, is characterized by pure electrostatic stress unqualified by spray discharge, thus leaving the repellent effort (which existed previously in another region, under restraint) 'free to manifest itself without re straint upon those particles conductively responsive thereto. I effect this by providing an electrode E which "also serves as a shield or screen, between the electrodes E and E. This screen-electrode is charged with electricity of the same sign as that of the spraying electrode E, and serves not only as a static-stress producer, to efiect repulsion of particles by its action in conjunction with the electrode E, but also as a shield to prevent the spray discharge'from the electrode E from continuing to bathe.

the surface of E and the particles thereon. The electrode E receives the spray from E on its back, and is thus charged, so that no other source'of charge need be connected with the electrode E provided it be made electrode to produce a static field and .assist and E of such material, or have such a surface, as

.will conduct the charge received from E over the surface of E and to the face thereof which is presented to the electrode E,

and provided also that the electrode E be suitably insulated from the ground and from other parts of the machine. A. metal screen will serve the double function of screen to catch the spray discharge and of functionally in effecting a repulsion of particles from the opposite electrode E. A less active conductor than metal, may be employed, but a degree of conductivityhigh as compared with the insulators or dielectrics, is necessary to. the effective production and maintenance of the static field between E By preference, also, I construct this screen E so that it presents a relatively broad surface (as compared with the electrode E) in parallelism to the surface of the electrode E immediately opposed thereto.

The, spray which proceeds from the electrode E is interrupted by the screen E which, so to speak, casts an electrical shadow upon the electrode E. The condi tion of the entire field is illustrated in Fig. 2 where s is that portion of the spray Which is playinguninterruptedly upon the surface of the electrode E while the portion 8 is intercepted by the screen E Between the screen E? and the electrode E the electrostatic field is characterized by substantially pure stress. Moreover, as the screen E is.

of conducting material, insulated at its'supports, the charge transferred'by the spray portions 8 flows over the surface; of the screen on all sides thereof and raises the and E is correspondingly more intense than would be the case if the screen E were as distant from the electrode E as is the electrode E. I

The particles of the material M pass from the region of spray 8 into the screened region. The poor conductors retain the spray-deposited charge and remain there fore in close adherence to the electrode E, While the better conductors, being relieved from the restraininginfluence of the spray, transfer the spray-applied charge to the electrode surface and respond at once to the, repellent eflort (previously felt by such particles but counteracted by the spray charge). and fly from the electrode E to be received and collected in some suitable receptacle. The screen electrode E? thus, in

association with the electrode E, exerts a repellent efiort sufficiently powerful to disengage the better conductors from the surface of the electrode E. The operation of that portion of the described apparatus which consists of the opposed faces of electrodes E and E is the same in substance and efi'ectas that of the opposed electrodes The gist of the process above described rests in the different rates of leakage of charge from particles on the material-receiving surface to the surface. In the sprayaifected region the spray-charge is showered upon all the particles of the mixture, and

the conductivity of some of these. may be so.

perfect that they deliver their spray-derived charges to the material-receiving surface instantaneously, so that while in the sprayaffected region they repeatedly leave the -surface orrise 011 it, only-to here-charged by .the spray and thrust back. Such particles, as soon as the conveying surface removes them from the spray-affected-region, will respond promptly to the electrostatic repellent effort andbe emphatically discharged from the mixture. Other particles, less conductive, willrequire a longer time for surrender of the spray-deposited charges ating effect; the particles are freed electrostatically from contact with the surface and association with close-clinging particles of vary low conductivity. There is no portion I of an electrode such as E whereon there is no charge, while the apparatus is electrically excited. The electrode E may be grounded, but this will not alter the fact that it is charged at all points of its surface, the density of field being greatest at the region nearest the electrode E (and E and least on the side away from these opposed electrodes.

The behavior of a mass of differentiated particles is indicated in Fig. 2, where dividers D and D are shown to define different regions of liberation or discharge of particles from the electrode E. Very good conductors are repelled from the region affected by the screen E and-show a trajectory which visiblydemonstrates the electrostatic repulsiomand the coaction of directionally divergent forces, namely, the electrostatic repulsion and gravity. These .particles fall between the screen E and divider D. r I

Less conductive particles, delivering their spray-deposited charges more slowly to the electrode E, cling thereto until their charges are effectually neutralized. When these charges are neutralized, the counter charge creeps from the electrode E to the particles, which are thereupon repelled. These par- I ticles are shown as leaving the electrode be tween the dividers D and D.

i As, in the illustration given by the drawings, this second class of conductors happens to leave the electrode.E from a region where the surface thereof is nearly horizontal, these particles appear merely to fall by gravity; the liberation of the particles from the surface and from the other ingredients of the mixture is, however, initiated and assisted by electrostatic repulsion, exerted in thedirec- 'tion of gravitational pull, so that the path or trajectory is substantially the same as it .would be were the particles liberated by gravity alone. The persistently clinging particles of poor conductivity will, in practice, be removed from the electrode E, by a brush, as B, or by other effective means.

The progressive liberation of particles therefrom, and yet be not so rapid as to convey particles destined to liberation at one selected region into the next region. Thus it will be found desirable to rotate the electrode E at different speeds for different material mixtures, or to shift the positions of dividers, as D, D; orto provide for both these variations in adjustment of the apparatus.

Referring to Fig. 3, the barrier E is shown as provided with insulating blocks, 6 which should be provided as E is made of conductive material. These blocks is rest on the frame F, (which is shown at one end only of the apparatus, in Fig. 3, the frame at the other end being partly omitted). Variations in rotation of the electrode E may be secured by the cone pulleys e and e and belt B. The dividers D, D, may be mounted, as here shown, on a base B.

grooved at b; the lugs, d, d, on the dividers fitting and. sliding in the grooves b, for the purposes of adjustment of the dividers.

What I claim and desire to secure by Letters Patent is:

1. The method of separating particles of comminuted material difierentiated as to fused spray discharge, and shielding an other part of said surface by intercepting a portion of the effective spray discharge, thus allowing the repelling effort on the shielded part of the surface to set free the more conductive particles, and thereafter separately collecting the difi'erentiated, components of the material.

2. The method of separating particles of comminuted material difi'erentiated as to electrical conductivity, which consists in. .conveying the particles in contact with a conductive surface, first spraying the particles while. so conveyed, with an electric spray discharge, thereafter removing the particles by the said conveyance, out of the spray-discharge, and subjectin themto the stress, whereof the conveying surface con,-

- action of a'field of substantial y pure static I stitutes one electrode, thereby repelling the 'better -conductive particles from' the conveyer electrode, and subsequently collecting the separated particles.

3. The method of separating particles of comminuted material differentiated as to electrical conductivity, which consists in conveying the particles in contact with a conductive surface charged with electricity of one sign, first spraying the particles while so conveyed with an electric spray discharge of an opposite sign, th reafter removing the particles by the said conveyance out of the spray discharge and subjecting them to the action of a field of substantially pure static stress, whereof the conveying surface constitutes one electrode, thereby repelling the better conductive particles from the conveyer electrode, and subsequently collecting the separated particles.

4. T he method of separating particles of comminuted material differentiated as to electrical conductivity, which consists in conveying the particles in contact with a conducting surface, first spraying the particles while so conveyed, with an electric spray discharge, intercepting part of said spray discharge, and converting it into static charge, thereby producing a field of substantially pure static stress betweensaid converted charge and the conveying surface, removing the sprayed particles out of the spray discharge and into the said staticstress field, thereby repelling the better conducting particles from the conveyer elecelectrode surface a diffused spray discharge,

and shielding another part of said surface by intercepting a portion of the effective spray discharge to allow a separation of the trode, and subsequently collecting the sepa- 4 differentiated particles in accordance with the nature of their differentiations.

6. The method of separating differentiated particles of comminuted material which consists in passing them through an electrostatic field in contact With an electrode surface opposing the repellent efiort of part of the electrode surface by directing thereon a diflusedspray discharge, and

shielding another part of said surface by intercepting a portion of the effective spray discharge, thus allowing the repelling effort on the shielded part ofthe surface to set free the differentiated particles the more susceptible to its influence, and thereafter separatel collecting the remaining particles.

Signed by me at Boston this eleventh day of December 1907.

HENRY AZOR WENTWORTH.

Witnesses CHARLES D. WooDBnRRY', ODIN ROBERTS.

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