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Title: Process for high temperature treatment of materials
Description: Description:
BACKGROUND The field of the present invention is the art of pyrometallurgy, particularly processes for high temperature treatment of particulate material by subjection to the action of an electrical discharge arc. The prior art concerned with such processes teaches that in order to achieve a complete and controlled changed in materials subjected to the action of electrical discharges, all such materials must pass through the zone of discharge and their time of residence in this zone must be of a certain controlled duration. In an effort to accomplish such control, use has been made of an arc spread into a fan-like shape, known as an expanded arc. Methods of obtaining and expanding an arc column were known before the Second World War and described by W. Weizel and R. Rompe in "Theorie Elektrischer Lichtbogen und Funken" (Leipzig, Barth, 1949), however such methods, although of scientific interest, do not lend themselves to industrial exploitation. The inevitably high thermal losses in the rotating cylinder and inability to inject sufficiently large quantities of feedstocks without affecting the stability of the discharge proved the main obstacles preventing industrial utilization of such devices. SUMMARY OF THE INVENTION A preferred apparatus by which the process of the present invention is carried out is the plasma arc furnace disclosed in my copending allowed application Ser. No. 225,892 filed Feb. 14, 1972. The illustration and description of the apparatus, its operation and functions as given in that application are incorporated herein by reference as matter essential to an understanding of the process comprising the present invention. The invention which is the subject of this application is a process for high temperature treatment of particulate material in an expanded electrical arc column moving in a closed arcuate path. The particles of the material may be of any individual size and shape compatible with conditions imposed by structure of apparatus by which the process is practiced. The term "treatment" as used herein includes calcinating, roasting, smelting, melting and refining of metals in general, comminuting, spheroidizing, coating, chemical reactions including the reduction and separation of ores, compounds of nonmetallic elements, formation of compounds of the hard metals, and any use to which the apparatus of my aforesaid application may be put. The process comprising the present invention is carried out by the steps of: establishing an electrical discharge arc column having upper and lower terminals, moving the column through a closed arcuate path, expanding the column during the course of its travel along the path, passing particulate material through the expanded column at an angle such that the particles comprising the material pass into and through the column in spiral paths which substantially prolong the period of their residence in the column, and collecting the arc treated particles emerging from the column at a point of deposit spaced below the lower terminal of the arc. The longitudinal axis of the arc column may be either vertical or inclined from the vertical. The locus of either arc terminal may optionally be at a movable electrode or a fixed electrode. If one is at a fixed electrode, the other must be at a movable electrode, and vice versa. In either case, the terminal of the arc at the movable electrode is moved by and with that electrode, and the terminal of the arc at the fixed electrode moves on and along the fixed electrode sliding longitudinally thereon. Various reactant substances may be entrained in the arc column to effect selective chemical treatment of particles in addition to the heat treatment of the arc. Other treatment substances and atmospheres may be introduced at various stages of the process as additional steps. DETAILED DESCRIPTION In its simplest form, the process of the present invention is carried out by establishing a continuous electrical discharge arc column, moving the column bodily through a closed arcuate path, passing particulate material into and through the moving column at an angle thereto such that the particles of the material in passing through the column travel in spiral paths between their points of entry into the column and their points of exit therefrom, and collecting the arc treated particles at a point of deposit after they emerge from the moving column. In the preferred mode of practicing the invention, the arc column is initiated and maintained as a plasma stream arc inclined with respect to the vertical. It discharges between an upper electrode moving in a closed circle path and a stationary lower electrode which provides a concentric closed circle path along which the lower terminal of the arc moves in correspondence with movement of the upper electrode. After the arc is struck, it is expanded to a fan-like shape by moving the upper electrode through its circle path and also by moving it upwardly to increase the vertical spacing from the stationary electrode. As a result of the combined movements of the upper electrode, the plasma stream arc revolves in its entirety through a path which has the geometric configuration of a frustrum of a cone, so that the expanded arc becomes, in effect, an inclined, continuously revolving, sector-shaped curtain. During revolution of the plasma stream arc, particulate material to be treated is fed downwardly into the upper end of the stream in which it is entrained and carried by and with the arc until it has passed entirely therethrough. Due to the revolving movement of the arc, and its inclination, each particle of the material travels down the arc in a spiral path which substantially prolongs its period of residence in the plasma stream. This prolongation is a salient feature of the process. After emerging from the under face of the plasma stream, the treated material is deposited in a refractory crucible in which it may be subjected to further treatment. The process optionally includes other steps by which, in combination with the electrical arc discharge, various other treatments affecting the nature and composition of the treated material may be effected; for example, oxidizing, reducing or neutral atmospheres may be introduced into the treatment zone or zones, chemical reactants may be introduced in the plasma stream or elsewhere, and rapidly expanding cold gases which are non-reactive with injected substances may be introduced for rapid quenching of reaction products; gases may be withdrawn from atmospheres resulting from action of the arc on the material being treated; various powders and fluids may be introduced into the plasma stream. Other info: Inventors: Tylko, Jozef Kazimierz (Faringdon, EN) Application Number: 462403 Filing Date: 1974-04-19 Publication_date: 1976-01-13 Assignee: Tetronics Research and Development Company (Faringdon, EN) Primary Class(es): 75/10.21 75/10.19, 219/129, 373/23 Other Classes: US Patent Ref:
Other Refs: Primary Examiner: Rosenberg, Peter D. Assistant Examiner: Attorney: Dennison, Dennison, Townshend & Meserole |
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