Classifying – separating – and assorting solids – Electrostatic
Reexamination Certificate
1999-08-26
2001-11-27
Nguyen, Tuan N. (Department: 3653)
Classifying, separating, and assorting solids
Electrostatic
C209S012200, C209S137000
Reexamination Certificate
active
06323451
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to the material separation art and, more particularly, to a particle separation system that uses a plurality of multistage separators in parallel to simultaneously separate two species of particles in a highly effective and efficient manner.
BACKGROUND OF THE INVENTION
Various types of apparatus for removing particles from a dry fluid flow using electrostatic separation techniques are well known in the art. An early example of such an apparatus is shown in U.S. Pat. No. 3,493,109 to Carta et al., the operation and limitations of which are described in detail in commonly assigned U.S. Pat. No. 5,755,333 to Stencel et al., issued May 26, 1998. Generally speaking, the Carta et al. patent relies upon turbulent flow and particle-wall contact in the separation chamber to electrostatically charge the particles. The particles are then drawn from the flow by opposed electrically conductive plates having opposite polarities.
While the apparatus proposed in the Carta et al. reference is somewhat effective for separating particles having a selected charge from a particle mixture, several significant limitations remain. For instance, no effective means is disclosed to ensure that once separated, the selected particles will be directed to the appropriate collection device. To the contrary, the apparatus disclosed in the Carta et al. patent promotes turbulent flow in the separation chamber, which can allow deleterious re-mixing of the particles to occur after separation. As should be appreciated, this reduces efficiency to the point that several cycles or passes through the apparatus may be required to achieve separation. In addition to reducing efficiency, multiple passes significantly increase the particle abrasion to which the wall of the apparatus is subjected thereby reducing the service life of the separator.
In an effort to overcome this shortcoming, commonly assigned U.S. patent application Ser. No. 08/726,255, entitled “Apparatus and Method for Triboelectrostatic Separation,” proposes an improved apparatus for separating two species of particles from a particle mixture with greater efficiency and effectiveness by using a curtain gas flow to carry the selected particles drawn from the mixture to a collector for recovery. Similar to the apparatus proposed in the Carta et al. patent, separation is effected through the use of oppositely charged conductor plates connected to a variable voltage source. The charged plates attract oppositely charged particles away from the mixture and towards the sidewalls of the separation chamber. The curtain gas flow (which is initially devoid of particles) is then introduced into the separation chamber to provide the cleaning action necessary to remove or sweep the particles from the plates for recovery.
While this apparatus is effective for separating two particle species from a particle mixture, it should be appreciated that further improvements in separation effectiveness and operational efficiency are still possible. More specifically, there is a need for an electrostatic separation apparatus that: (1) reduces turbulence in the separation chamber(s) to ensure that more selected particles are separated from the particle mixture and collected for recovery; (2) includes separators having one or more relatively compact modular separation stages that each include a pair of separation chamber(s) having one or more elongate electric field zones which are capable of handling relatively high flow velocities to allow for an increase in the amount of the particle mixture processed per unit of cross-sectional area; and/or (3) includes a plurality of separators arranged in parallel to ensure that the particle species are fully separated in a single pass to improve operating efficiency and greatly increase the amount of the particle mixture processed in a given time period.
SUMMARY OF THE INVENTION
Accordingly, it is a primary object of the present invention to provide an improved apparatus for electrostatically separating two species of particles from a particle mixture that overcomes the above-identified limitations and shortcomings of the prior art.
Another object of the present invention is to provide a particle separation system including a single distributor for simultaneously supplying a particle mixture to a plurality of parallel separators having at least one separation stage and forming an electrostatic separation apparatus, whereby two distinct and substantially pure particle species are recovered from said apparatus.
Still another object of the present invention is to provide an electrostatic separation apparatus having one or more separators that include multiple separation stages in series that each use curtain gas flows to collect selected charged particles drawn from a particle mixture by an electric field in a separation chamber, whereby after passing the particle mixture through said multiple separation stages, two distinct and substantially pure species of particles are fully recovered.
Yet another object of the present invention is to provide an electrostatic separator that is adapted to straighten the particle mixture and curtain gas flows to reduce turbulence in the separation chamber and improve separation efficiency.
A further object of the present invention is to provide an electrostatic separator having a separation chamber divided into first and second separation subchambers each having an electric field zone for simultaneously separating selected charged particles from a stream of a particle mixture flow.
Still a further object of the present invention is to provide a modular separation stage for use alone or in a multistage separator that effectively separates higher feed rates of a particle mixture per unit of cross-sectional area of the separator than heretofore possible.
Additional objects, advantages and other novel features of the invention will be set forth in part in the description that follows and in part will become apparent to those skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing and other objects, and in accordance with the purposes of the present invention as described herein, a particle separation system is described that includes an electrostatic separation apparatus. In the broadest aspects of the invention, the electrostatic separation apparatus includes one or more parallel separators having at least one, and preferably a plurality of modular electrostatic separation stages. Each stage is designed to handle a higher feed rate of a particle mixture flow than previously possible by handling a relatively high flow velocity (>10 m/s) and having separation chamber(s) with greater horizontal cross-sectional areas. Dual simultaneous processing of the particle mixture flow in each stage is also made possible by a center partition that divides the separation stage itself in two. This partition thus creates dual streams of the particle mixture for delivery to first and second subchambers in each separation stage. Each subchamber includes a relatively short and narrow electric field zone created by pairs of elongate parallel conductor plates. Selected charged particles drawn from the mixture in each subchamber by the electric field are entrained by a curtain gas and carried away for recovery, while the remaining dual streams of particle flow are passed on to the next-in-line separation stage for further processing. Advantageously, by simultaneously processing dual streams in a rapid fashion through multiple stages, a high feed rate is achieved. Even though each stage may only remove a small percentage of the selected charged particles because of the relatively short and narrow separation zone, separation efficiency is not compromised because of the use of a large horizontal cross sectional area and processing across
Ban Heng
Finseth Dennis
Neathery James K.
Schaefer John L.
Stencel John M.
King and Schickli PLLC
Nguyen Tuan N.
University of Kentucky Research Foundation
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