Classifying – separating – and assorting solids – Stratifiers – Movable bed
Reexamination Certificate
2000-02-17
2002-08-27
Nguyen, Tuan N. (Department: 3653)
Classifying, separating, and assorting solids
Stratifiers
Movable bed
C209S488000, C209S643000, C209S919000, C494S058000, C494S063000
Reexamination Certificate
active
06439394
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to separation of dry powders, more particularly it relates to a centrifugal separator for continuous separation of dry powders.
At present, several methods are utilized for dry separation of powders including: air separation, vibration separation using batteries of sieves, and vibro-gravitational separation. In air separation systems, separation is realized by air jets, which remove fine particles out of powder flow and transfer them to a hopper, and heavy particles, which are not carried out by an air jet, fall into another hopper.
2. Description of Related Art
U.S. Pat. No. 5,934,483 to KOLACZ discloses an apparatus of the forced air vortex type for classification of particulate material into a fine portion and a coarse portion, the apparatus comprises a truncated cone shaped upper section having a separating wheel rotating about a substantially vertical axis, a vertically arranged inlet pipe for supplying a particulate material dispersed in an air flow, a conical feed distributor having a tip end directed downwards and arranged concentrically with the inlet pipe and the separating wheel, and a spiral shaped outlet for removal of classified fine material dispersed in air, and a substantially truncated cone shaped lower section, the upper section of which exhibit a secondary air inlet arranged tangentially to the circumference of the lower housing to supply secondary air in a direction concurrently with the direction of rotation of the separating wheel and a second outlet for classified coarse particulate material.
U.S. Pat. No. 4,869,786 to HANKE discloses a process and an air classifier for the separation of classifying material into coarse material and fine material. Known air classifiers suffer from considerable deficiencies with regards to the throughput and the separation efficiency. To avoid this, the device provides for the performance of a separate reclassification, which takes place in the same way as the pre-classification, whilst incorporating mechanical centrifugal rejection of coarse material particles, particularly through the impact ledges of a centrifuge basket.
U.S. Pat. No. 3,941,687 to PETERSON discloses a solids separation system designed for pneumatic separation of pieces of scrap particularly metallic scrap, into light and heavy fractions. The mixture of pieces of scrap is fed into an enclosed separation vessel wherein they fall by gravity into a horizontally directed stream of air blown into and across the separator vessel, whereby the heaviest pieces fall through the air stream into a heavy solids hopper and the lighter materials are carried downstream by the force of the horizontal air stream into a second hopper. A gas outlet port is provided at the top of the vessel thereby imparting an upward velocity vector to the gas. The horizontal velocity of the gas being reduced by expansion, light metal pieces fall out of the influence of the gas stream into the light solids hopper. Means are provided for adjusting the air flow path from the first into the second hopper comprising a pivoted angularly disposed baffle plate defining the rear wall of the first hopper, the surface of which plate also serves to direct solids intercepted thereby into the first hopper.
These methods are energy-consuming due to the necessity of continuous maintenance of air flows. Considerable air volumes become saturated with dust and require special air-cleaning equipment, which makes the facility awkward and expensive.
Separation using sieves has proven to be cheaper and ecologically cleaner. For example, U.S. Pat. No. 3,932,442 to SALMON discloses a process for screening materials as a function of particle size differences by feeding the materials onto one side of a substantially planar screen and vibrating the screen by producing a translational screen oscillation in directions normal to the screen plane and a torsional screen oscillation about an axis normal to the screen plane so that each point of the screen moves in a helical path. Screened material is collected at the other side of the screen and screened retentate is transported by the torsional screen oscillation to an exit port at a location spaced from the axis of torsional oscillation. The process is particularly applicable to shipboard or other mobile use, since the spring stiffness provides good structural support under tilt or side acceleration conditions.
This method is efficient for medium particle sizes in the powder where di>50 &mgr;m. However, at smaller particle sizes, the sieves are soon clogged up. The result is that the process efficiency abruptly decreases. Additionally, elongated particles with one of cross-sections corresponding to the mesh size of the sieve are undesirably allowed pass through the sieves.
Vibro-gravitational separation consists in a motion of particles of different sizes, densities or shapes under the action of vibration along different paths over an inclined concave. Sometimes numerous holes are made in the concave for the passage of compressed air supply, in order to increase the amplitude of particle jumps. This method has proved to be rather efficient for separating seeds and coarse-grain powders. However, its efficiency for powders with a medium particle size below I 00 pm is rather low.
The facility or device suggested in the application PCT/US 98/15797 and International Publication Number WO99/0747, the disclosures of which are expressly incorporated by reference in their entirety herein may be employed as a starting point for the system of the present invention. A separator proposed in this application operates cyclically. The powder is fed to the center of horizontal rotating disk, which spreads it along the entire Internal wall of a rotating cup. Dry powder is separated into two fractions on the internal wall of a rotating cup under the action of friction force and centrifugal force on each particle. Larger particles are allowed to pass over the upper edge of the cup, whereas smaller ones remain on the cup wall. However, to make particles fall down from the cup wall, it is necessary to stop the cup. After it stops, the action of centrifugal force on the particles is stopped, and they fall down into a respective hopper. In this state the facility is ready for the next separation cycle. The efficiency of such a separator has proven to be low, because a large share of operation time is spent on unproductive stops of an inertial cup. Moreover, due to multiple starts and stops, the service life of the engine or motor is shortened, and especially important, the power consumed per unit volume of separated powder is high because an electric engine consumes 2-3-fold amount of energy at the start than in the constant operation mode. Accordingly, improvement is still desired.
SUMMARY OF THE INVENTION
The present invention therefore provides a centrifugal separator for dry separation of powders having a high efficiency and a low power consumption due to its continuous operation. In other words, in the proposed separator the feeding of powder to be separated and the removal of coarse and fine powder fractions after separation take place simultaneously and continuously.
Powder separation occurs on a wall of a cavity of a rotating body. The body rotates around a vertical axis and has a centrally symmetrical cavity open from above and from below. The cavity symmetry axis coincides with the body rotation axis, and the cavity surface is a surface of revolution with circular upper and lower edge's of this cavity, the diameter of the upper circumference being greater that the diameter of the lower circumference.
Powder is fed to a certain zone which is designated a feeding zone and which is positoned adjacent to a lower portion of the cavity surface. The length of this zone is designed to be much less (at least by an order of magnitude) than the length of a separation zone, with the length of the separation zone being approximately 1s. The length (in meters) of the separation zone is determined by the relat
Eiderman Boris
Levy Haim
Voskoboinik Moshe
Greenblum & Bernstein P.L.C.
Nguyen Tuan N.
SorTech Separation Technologies, Ltd.
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