Classifying – separating – and assorting solids – Electrostatic – Attracting and repelling
Reexamination Certificate
2001-09-13
2004-04-20
Walsh, Donald P. (Department: 3653)
Classifying, separating, and assorting solids
Electrostatic
Attracting and repelling
C209S127100, C209S129000, C209S130000, C209S127400
Reexamination Certificate
active
06723938
ABSTRACT:
TECHNICAL FIELD
The present invention is concerned with a particle separator for the separation of particulate mixtures comprising species that exhibit difference in electrical conductivity and, more particularly, with the separation of particulate mixtures comprising species that exhibit difference in electrical conductivity through electrostatic separation.
BACKGROUND ART
Mineral separation plants used in the titanium mineral processing industry world-wide consist essentially of similar process technologies applied in a manner that is often tailored to an individual ore bodies separation requirements. Dependent upon a wide number of factors including particle size and shape, mineral grade, geology of the ore body, type of mineral species present and the physical characteristics of said mineral species, a unique recovery process is applied to optimise plant performance and satisfy operational and capital cost targets. Nevertheless, all titanium mineral processing plants in the world utilise similar process technologies applied in varying ways to accomplish their process needs.
Mining is carried out by firstly excavating the ore and subjecting it to gravity concentration which isolates the heaviest particles into what is termed a heavy mineral concentrate. The heavy mineral concentrates are sent to a dry separation plant, where individual minerals species (of which there may up to 20 or more present) are separated using their different magnetic, electrical or other physical properties, often at elevated temperatures. Separation equipment commonly includes but is not limited to, high-tension electrostatic roll (HTR) and electrostatic plate (ESP) separators, as well as gravity and magnetic processes. Using electrostatic separation techniques the conductors such as rutile and ilmenite are separated from the non-conductors such as zircon, quartz and monazite. These separators are extensively used for the separation of conductor and non-conductor mineral species typically found in the titanium minerals industry.
A wide variety of electrostatic induced charge and ionised field separators have been invented over the last 90 years however the devices of existing commercial designs described below have undergone little fundamental change in recent years.
Based on the charging mechanisms employed, three basic types of “electrostatic” separators include; (1) high tension roll ionised field separators (HTR), (2) electrostatic plate and screen static field separators (ESP and ESS herein called ESP) and (3) triboelectric separators. ESP and HTR separators are the most commonly used today although in recent times some interest has been directed towards triboelectric separators however their application remains limited to mineral species that can be contact charged and so they are suitable for separations of non-conductor species only.
Customarily, HTR separators utilise a grounded roll that transports the feed material through the high voltage ionising field (corona) which charges the particles by ion bombardment. Conducting particles lose their charge to the earthed roll and are thrown from the roll by centrifugal and gravity forces. Non-conducting particles are pinned to the rotor and are transported further around the roll before their charge either dissipates and they are thrown off or are removed by either mechanical means (brush) or high voltage AC wiper.
ESP separators have an electrode designed to generate a static field and the particles are charged by conductive induction. In their common form ESP separators utilise a stationary grounded surface such as a plate over which the material flows, forming the connection to ground that particles must have to allow them to become charged by induction. Triboelectric separators do not use the electric field to effect particle charging. Particle to particle and/or particle to surface charging occurs when particle species with different contact charging potential are brought into contact with one another. The particle charge attained can then be utilised to effect a separation in a static electric field.
These three basic separation types are often not present alone in any mechanism and the machine characterisation essentially refers to the predominant or major separating effect. The present invention relies primarily on conductive induction to charge the particles and so the operation of an ESP separator is described in more detail below.
ESP conductive induction separators customarily comprise a curved, inclined electrically grounded plate onto and over which a feed mixture comprising species which differ in their electrical conductivity (some being conducting species or “conductors” and other being non-conducting species or “non-conductors”) flows. The mixture is discharged onto this plate usually from a feed chute so that it travels over the plate due to gravity and in electrical contact with the plate surface.
The plate extends beside and below a high voltage electrode spanning the full width of the separation zone. The grounded plate is commonly curved, convex or “S” shaped, which provides good particle to plate contact when clean. Particles flowing over the grounded plate pass though the high potential electric field produced between the electrode and the plate itself whereupon a charge is induced into the conductive particles. These conductive particles acquire a charge of opposite polarity to the electrode whereas the non-conductive particles remain uncharged. The charged conductors are lifted off the grounded plate due to the physical attraction of oppositely charged bodies and are attracted towards the electrode.
Thus the conductors lift away from a gravitationally induced trajectory before falling through a splitter type collection means below and/or beyond the plates lower edge dividing the feed into a mainly conductor and a mainly non-conductor fraction.
The above description of the mechanism describes a one-stage separation process. Electrostatic Plate Separators (ESP) typically would incorporate 5 identical stages with up to two starts or individual streams being treated in one machine. Each new stage follows the last with material cascading from one stage to the next. Typically, conductors are gradually removed from the non-conductors whom continue on to the next stage for re-treatment.
Each stage is similar to the first with feed chute, grounded plate, electrode and splitter system duplicated and arranged one above the other in a vertical configuration. Adjustment of the splitters, electrode position and feed plate angle is typically done at each stage independently of other stages.
In the treatment of mixtures of particles with a range of physical characteristics including conductivity and particle size and density, it is necessary to adjust the relative positions of the feed plate, electrode and splitters to optimise the separation. It is usually necessary to adjust not only the air gap between plate and electrode but also the slope and shape of the plate and splitter positions independently on each stage. Voltage and polarity is traditionally similar over all starts and stages on each machine bank as a single high voltage power supply is used for simplicity reasons. A typical process in a plant may utilise many of these machines installed side by side or otherwise and if operating on the same duty, the operators would normally aim to set up electrode and splitter settings similarly for each machine.
There have also been proposals to use other than a grounded flat or curved plate, for example U.S. Pat. No. 2,258,767 discloses an electrostatic separating apparatus in which the grounded plate is formed into a roll. The roll rotates continuously and a portion thereof comes into appropriate juxtaposition with an electrode for conductive induction of charge in conducting species located on the surface of the roll. The invention is characterised in that the electrode is a rotatable cylindrical electrode and includes wiper means containing abrasive material co-operating with said electrode for polishing it as it rotates. At colum
Joerger Kaitlin
Moore & Van Allen PLLC
Skord Jennifer L.
Walsh Donald P.
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