Classifying – separating – and assorting solids – Electrostatic – Stratifying
Reexamination Certificate
1999-12-23
2002-12-24
Walsh, Donald P. (Department: 3653)
Classifying, separating, and assorting solids
Electrostatic
Stratifying
C209S129000
Reexamination Certificate
active
06498313
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to the material separation art and, more particularly, to a particle separation system, including an improved electrostatic separation apparatus, and a related method for electrostatically separating two species of particles present in a particle mixture.
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, 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 created by the mixing of the particle and curtain gas flows to ensure that more selected particles are separated from the particle mixture and collected for recovery; (2) enhances particle separation efficiency by permitting adjustments to be made to the length of the electric field during operation; and/or (3) includes serial separators in each apparatus to ensure that the particle species are fully separated in a single pass. Additionally, including a plurality of the electrostatic separation apparatus meeting these criteria in a system fed by a single distributor would improve operating efficiency and greatly increase the throughput or volume of the particle mixture that can be 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 the particle mixture to a plurality of individual electrostatic separation apparatus, whereby two distinct and substantially pure particle species are recovered from each apparatus.
Still another object of the present invention is to provide an electrostatic separation apparatus having multiple separators in series for removing and collecting selected charged particles from a particle mixture, whereby after passing the particle mixture through said multiple separators, two distinct and substantially pure species of particles are fully recovered.
Yet another object of the present invention is to provide an electrostatic separation apparatus that includes flow straighteners for both 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 separation apparatus having at least one separation chamber wherein the length of the electric field zone is selectively adjustable for varying the quantity and quality of the selected charged particles that are drawn from the particle mixture.
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, an improved electrostatic separation apparatus is disclosed and use of this apparatus as part of an overall particle separation system is described. In the broadest aspects of the invention, the improved electrostatic separation apparatus includes at least one separator having an electrostatic separation chamber. Preferably, the separator is cylindrical and has a first inlet that receives a particle mixture entrained in a dry driving fluid, such as air. The inlet is designed to create a spiraling, turbulent flow that assists in generating a differential charge on the two constituent species of particles present in the mixture prior to delivery to the separation chamber.
The separation chamber includes an electric field zone for drawing particles having a selected charge from the mixture. Specifically, a concentric electrode and conductor at different electric potentials are provided in the separation chamber to create a non-uniform electric field zone. A variable voltage source may be connected to the electrode and conductor to control the polarity and magnitude of the voltage applied to each. Alternatively, the potential difference may be created by connecting the variable voltage source to the conductor and grounding the electrode. Depending on the charge and amount of voltage applied to the conductor and the electrode, the difference in potential across the non-uniform electric field creates an electric field force vector that draws particles having a selected charge away from the particle mixture flow.
To remove or sweep the selected charged particles drawn from the particle mixture in the electric field zone, a flow of curtain gas is provided. Specifically, a curtain gas chamber concentric with the first inlet includes a first curtain gas inlet for supplying a first curtain gas flow to the separation chamber. The curtain gas entrains the particles drawn from the mixture and carries them to a first collector for recovery.
In accordance with an important aspect of the present invention, improved separation efficiency is provided by substantially
Ban Heng
Finseth Dennis
Neathery James K.
Schaefer John L.
Stencel John M.
King & Schickli PLLC
Rodriguez Joseph C.
University of Kentucky Research Foundation
Walsh Donald P.
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