US2072501A - Apparatus for electrostatic separation - Google Patents

Description

APPARATUS FOR ELECTROSTATIC SEPARATION Filed March l, 1935 G. GRAVE ET AL, I 2,072,50fi

Patented Mar. v2, 1937 2,072,501 v APPARATUS FOR nI g r nosrA'ric sErAnA- Georg Grave, FrankIort-on-the-Main-Heddernhelm, and Erich Oppen, Hanover, Germany, as-

signors to American Lurgi Corporation, New

York, N.-Y., a corporation oi New York Application March 1 1935, Serial No. 8,966

In Germany January 16, 1935 3 Claims.

This invention relates to an apparatus for electrostatic separation.

In the case of electrostatic separators operating on the attraction principle the attraction of 5 the particles takes place as soon as the electric force of attraction overcomes the other forces.

The invention will be explained with reference to the accompanying drawing in which Fig. 1 is a diagrammatic representation of the forces involved. in an electrostatic separator in whichthe particles are carried on one drum into an electrostatic field created by an adjacent .1. .1". and

Fig. 2 is a diagrammatic representation of the forces involved'in accordance with the invention.

If there exists an electrostatic field between the feeder drum I and the high-tension drum 2 (Fig.

1) the lifting of the particle A takes place as soon as the charge assumes such a value, that they sum of centrifugal force AB plus electrostatic force of attraction BC becomes greater than the force of gravity AD sin a. From the above itresuits that a good separation is not possible between two drums; since, the longer the particle remains on the revolving drum I, the more time is available to accumulate an electrical charge, and the stronger the electrical attraction will be. This is the reason why generally electrostatic action between two drums is only practicable 'if there are very great differences of weight between the particles which are to be separated.

- Fig. 2 shows a way to avoid these disadvantages and to enlarge the field of usefulness for those cases where the difference between power off attraction and time necessary for charging the 5 particles is only small. The material to be separated is fed through the channel 9 to the metallic drum I, which is grounded. The material to be treated is entirely shielded against the electrostatic field emanating from drum 2 by means 40 of two metallic drums 3 and 4, which are grounded, and the surfaces of sheet-iron or the like 5 and 6. Only the space between 3 and 4 is influenced by the electric field. Now, it is possible to adjust the drums 3 and 4 in such a manner 45 that only the particles which hardly take an electric charge or the particles which are easier to be attracted are lifted from drum i and go to receptacle 8, whereas the particles which are not attracted fall into receptacle 1. The path of 50 the lines of force is represented in Fig. 2. The

material to be treated coming from the space, en-

(Cil. 209-129) tirelyfree from force lines, on the left of drum 3, enters very suddenly an almost homogeneous field so that the attraction occurs equally suddenly.

Of course regulation may also be obtained by means of the revolving velocity of the drums. It is advantageous to run the drum 2 at such a rate of speed as to avoid the tailing back of particles lifted by it on to drum i. It has been attempted heretofore to obtain shielding by semi-conducting separating tongues. Leaving out of the question that this means of shielding really shields only part of the lines of force, these tongues have thedisadvantage, that they get clogged with material in continual service and the apparatus becomes incapable of functioning. This drawback is avoided by using revolving drums, which can be easily cleaned by means of scrapers. A further advantage of the invention consists in the fact that the device is protected against the chemical influence of the ozone, which forms inevitably, since no semi-conducting parts are used which, as is already known, often lose conductivity under the action of ozone.

We claim:--

1. Apparatus for electrostatic separation comprising a revolving grounded carrier drum, means for delivering the material to be separated to said carrier drum, a relatively high potential revolving drum spaced from said carrier drum serving to create a high potential electrostatic field between said drums, and two grounded revolving drums disposed at opposite sides of said field and serving to confine the electrostatic field operative on the material to the space therebetween.

2. Apparatus for electrostatic separation comprising a grounded revolving carrier drum, means for supplying material to be separated to said carrier drum, a revolving high potential drum spaced from said carrier drum and creating an electrostatic field through which the material on said carrier drum must pass, and means for shielding the material and confining said electrostatic field comprising grounded screening drums situated on each side of the space between said carrier drum and said high potential drum.

3. Apparatus for electrostatic separation as defined in claim 2 in which said screening drums are adjustable.

GEORG GRAVE. ERICH OPPEN.

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