US2174681A - Electrostatic separating apparatus - Google Patents

Description

0d. a, 1939. H w, BARTLETT 2,174,681

ELECTROSTATIC SEPARATING APPARATUS Filed Dec. 5, 1957 IN VENTOR.

ATTORNEY.

21W wa UNITED STATES PATENT OFFICE" 2,174,681 ELECTROSTATIC SEPARATING APPARATUS Harold W. Bartlett, Berkeley,

Rosenberg Bros. & (20., a corporation of Caliio Califi, assignor to San Francisco, Calif rnia Application December 3, 1937, Serial No. 177,950

2 Claims.

This invention relates generally to apparatus for effecting separation between fractions of divided material, in accordance with diiferences in electrical characteristics, such as diflerences in conductivity or dielectric value. More particularly the invention relates to apparatus of the type making use 01' an electrostatic field, created by electrical charges impressed upon spaced electrodes, and between which the material is caused to pass, in efiecting a separation.

Apparatus of the above character have been known for many years, but their commercial applications have been limited. Use of a high potential electrostatic field for the removal of dust particles from air, as for example for removing smoke from flue gases, has achieved considerable commercial success. .However, at-- tempts to apply somewhat the same principles to separation between fractions of solid materials, have not met with commercial success. I attribute this largely to the manner in which the materials have been subjected to the-electrostatic field, and to the absence of a proper arrangement whereby the separating action could be stabilized and made uniform.

It is an object of the present invention to provide an apparatus which can be successfully applied in many industries,.to separate fractions of solid material having different electrical characteristics, as for example differences in conductivity, dielectric strength or both. In attaining this object I have provided an arrangement whereby the material being subjected to the electrostatic field is dropped in free falling fashion through a separating zone, and whereby the electrodes are fso arranged and are of such a character as to produce a comparatively constant electrostatic separating action.

Further objects of the invention will appear from the following description in which the preferred embodiment of the-invention has been explained in detail in conjunction with the accompanying drawing.

Referring to the drawing:

Fig. 1 is a side elevational view, illustrating in diagrammatic fashion, apparatus incorporating the present invention.

Fig. 2 is a cross-sectional detail taken along the line 2-2 of Fig. 1.

Fig. 3 is a schematic circuit diagram, to facilitate an understanding of the invention, and to show 'the manner in which the electrodes are connected to a source of high unidirectional potential. v

The apparatus comprising the present inven- (c1. zo9 130) tion makes use of an arrangement of electrodes, source of unidirectional The electrodes are adapted to laterally directed electronic wind through a zone of separation. Suitable conveying means serves to drop thematerial to be separated into the zone of separation, where it is acted upon by the electronic wind, to eifect a separation in accordance with difierences in electrical characteristics. Below the zone of 10 separation suitable collecting means is provided, as for example bins or receptacles into which the two or more separated fractions fall.

Referring to the drawing I have shown generally upright electrodes Ill and il,which are disposed upon opposite sides of a separation zone A. Electrode Ill may .vary 8.5110 structural details, but in this instance it is formed of wire screening, with the metal points l2 extending from one side of the same. Any suitable mounting can be provided to support this electrode, as for example the high tension insulators l3, and frame It.

Electrode ll may also vary as to details, but in this instance it is likewise a wire screen. The *2 foraminated nature of such a screen appears to facilitate maintenance of the desired ionic wind. While electrode 1 I may be stationary in the same manner as electrode in, it is desirable in the handling of certain materials, to form high potential. create a i the screen as an endless belt, carried by the insulated pulleys or rollers I 6, l1 and I8. At one point the belt is shown being engaged by a rotary cleaning brush l9. When in operation one of the rollers supporting the electrode II, as for example roller i1. is rotated at a slow speed from a suitable source of power, and the brush is is likewise driven to remove any particles adhering to the electrode. A terminal 2| is shown for making electrical connections with the electrode l0, and likewise suitable provision is made for making electrical connections with electrode I I as for example .a contacting roller 22, which connects with the terminal 23.

Assuming that oppositely directed potentials are placed upon the electrodes l0 and H, electrode lli creates the effect of so-called electronic wind in a direction laterally across the separating space A.- One might expect the plane of neutral potential of the electrostatic field between electrodes l0 and II, to be about midway between these electrodes. However, tests have shown that without supplemental means as will be presently described, the neutral plane appears to be shifted to a position in proximity symmetrical field has been found to seriously interfere with uniformity of separating action.

The meanswhich I utilize to stabilize the electrostaticfield, and to shift the neutral plane to a region substantially mid-way between the electrodes l0 and H, makesuse of a neutralizing electrode 24. This electrode can be'formed of wire screening, with its one side provided with the metal points 26. It is shown carried by a suitable support means, such as the insulators 21 and supporting frame 28. A suitable terminal 29 is provided for making connection to the high potential energizing system. To facilitate making adjustments, frame 28 can have adjustable connections 3i, with the main support frame 32,

The means for supplying material to the separating zone A, can consist of suitable conveying means, such as a shaker conveyor 33. The discharge end of this conveyor is disposed above the separating zone A, so that as material drops from the end of the conveyor, it progresses do nwardly in free falling fashion, substantially as a sheet. Below the separating zone A a plurality of separate receivers 34, 35 and 36 are provided. These receivers may...connect with the associated conveying conduits 38, 39 and 40.

The manner in which electrical connections are made can be best explained by reference to Fig. 3. A high potential transformer 42 is connected with some suitable source of alternating current, and the high potential secondary of this transformer connects with a rectifier 43. Leads L1 and L2, from the high potential'secondary side 'of rectifier 43, connect respectively to the electrode Ill, and to the electrodes II and 24. Recti-- fier 43 can be of the electronic type, 'afiording a unidirectional pulsating output. A mechanical commutating type of rectifier can also be used, in which case the unidirectional output pulsates with a substantially flat topped wave form. With the electrode l0 measuring in the neighborhood of 1,500 square inches, and electrodes l0 and H placed apart a distance in the neighborhood of 18 inches, a potential in the neighborhood of twenty thousand volts gave good results.

- In the past I have used the apparatus described above on various food products, including raisins for the purpose of separating raisins from leaf and stem material, unmilled rice for the purpose of separating ricefrom water cress seed,

and on shelled nuts like almonds for the purpose of separating the meat of the nut from shell material. In employing the apparatus described above, for the treatment of a material such as raisins, the raisins are 'supplied'from conveyor 33, and permitted to drop in free falling fashion down into the separating zone A. The raisins are deflected only slightly by the ionic wind created within the separating zone, but the stem and leaf material, because of a difference in dielectric value and conductivity, as compared to the raisins, are deflected to a considerable extent so that below the separating zone, the raisins fall in one collecting receiver, while the stem and looseleaf material fall into one or more separate receptacles. In the treatment of unmilled rice it is desirable to first pass the rice through a suitable machine for removing the beards from r with one 'of the electrodes. The resulting nonthe rice kernels, after which the rice is likewise supplied by the conveyor 33, and permitted to drop down through the separating zone. The water cress seed is deflected laterally by the ionic wind to an extent substantially greater than the rice kernels, so that the rice kernels fall in one receptacle, while the seeds fall in another receptacle. Substantially the same separating action is exerted upon shelled nuts such as almonds, in which case the shell material or fragments of the hull are deflected to a greater extent than the meat of the nut.

In the handling of materials as described above, small light material, such as pieces of stem or leaf material, or beards from rice, may adhere to electrode H, and tend to set up a counter electronic wind. It is for this reason that electrode II is preferably in the form of an endless belt, whereby such material is continuously removed by the brush l9. .s

The particular manner described above for constructing the electrode Ill, is relatively simple and effective. However, in place of such electrode, I have used relatively fine wires stretched parallel about two inches apart, and without the metal points 12. Such fine wires seem to have the ability of creating a laterally directed ionic wind.

In certain of my operations the conveyor 33' has been made of metal and grounded. In other instances I have electrically connected. conveyor 33, to one side of the high potential supply, particulariy the side to which electrode I0 is connected. This serves to impart an initial charge to the material as it falls from the conveyor 33, thereby augmenting the electrostatic forces tending to displace the material laterally.

I claim:

1. .In apparatus for separating divided material in accordance with differences in electrical characteristics, means for maintaining an'ionic wind through a zone of electrostatic separation, said means including an electrode at one side of said zone and adapted to induce an ionic wind away from the same and through said zone, a foraminated electrode at the other side of said zone, and a third electrode behind said foraminated electrode and equipped with conducting points directed towards the second electrode, and means for causing material to be separated to pass through said separating zone.

2. In apparatus for separating divided material in accordance with diiferences in electrical characteristics, means formaintaining an ionic wind through a zone of electrostatic separation, said means including a pair of electrodes disposed on opposite sides of said zone and adapted to be charged with oppositely directed electrical potentials, one of said electrodes being provided with conducting points directed towards said zone and the other of said electrodes being foraminated, and a neutralizing electrode behind said foraminated electrode, whereby the neutral region of said zone is shifted to a region substantially mid-way between said first-named electrodes, said neutralizing electrode being likewise provided with conducting points directed towards said separating zone, and means for supplying material to be separated to said zone.

HAROID W. BARTLETI.

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