Direct smelting process with a thermal plasma

Details Direct smelting process with a thermal plasma Direct smelting process with a thermal plasma

1990-09-26

1993-09-14

Andrews, Melvyn J..

Specialized metallurgical processes, compositions for use therei

Processes

Electrothermic processes

75 1021, 75 1022, C22B 922

Patent

active

052444880

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a process for directly smelting ores and metal compounds with a thermal plasma.


BACKGROUND ART

Recently, attention has been directed to the direct smelting process wherein an ore or metal oxide is reduced in a molten state or thermally decomposed with use of a thermal plasma produced by arc discharge to directly obtain a metal or a product enriched in metal.
The direct smelting process attracts attention because of its advantages. When the thermal plasma is used for smelting, a superhigh temperature is obtained which can be maintained with good stability, giving rise to a reaction which requires such a high temperature as is not available with usual heat sources. Since the reaction velocity increases exponentially with temperature, the reaction can be carried out within a shorter period of time with use of an apparatus of smaller size.
As disclosed in U.S. Pat. No. 3,856,918 and Examined Japanese Patent Publication SHO 60-53088, the direct smelting process is practiced by causing arc discharge across a cathode and an anode, and feeding a powder of ore or the like along with a plasma forming gas to melt and decompose the powder while it is passing through a plasma arc, or feeding the powder around a plasma arc to melt and decompose the powder by the radiant heat of the arc. To produce a reducing gas in this process, hydrogen, methane, carbon monoxide or like reducing gas is used as the plasma forming gas along with an inert gas. As disclosed in Examined Japanese Patent Publication SHO 53-44128, it is also known to coat the particles of the powder with a layer of carbonaceous substance in order to effect accelerated reduction.
With the above techniques, however, it is impossible to retain the particulate ore or the like in or around the plasma arc for a sufficient period of time, making it difficult to reduce the material in a molten state or decompose the material and therefore necessitating a cumbersome pretreatment such as the adjustment of the size of particles or coating of the particulate material with a carbonaceous substance.
Further to produce a stabilized plasma arc for a reducing reaction, the process requires a large quantity of hydrogen,argon, methane or like gas as the plasma forming gas.
Additionally, the plasma generator requires means for cooling the electrodes and means for feeding the plasma forming gas and the particulate material. These means render the apparatus complex and result in an increased smelting cost along with the use of large quantity of the plasma forming gas.
An object of the present invention, which has been accomplished in view of these problems, is to provide a direct smelting process which can be practiced easily by simple equipment regardless of the form of material to be smelted and without using any plasma forming gas.


DISCLOSURE OF THE INVENTION

The present invention provides a direct smelting process wherein an ore or metal oxide is melted and reduced or thermally decomposed by a thermal plasma having a reducing atmosphere to obtain a metal or product enriched in metal, the direct smelting process being characterized in that a polyphase current voltage is applied to a multiplicity of graphite electrodes to cause arc discharge in air and produce a strongly reducing nontransferred plasma arc due to the resulting oxidation decomposition of the graphite electrodes, the plasma arc being jetted out from the tips of the electrodes directly against the ore or metal oxide for smelting. In this case, the multiplicity of graphite electrodes are in an inverted conical arrangement so that their tips are approximately equidistantly spaced apart on a substantially circular line, whereby the nontrasferred plasma arc can be forced out concentrically from the tips of the electrodes with ease.
In practicing the present invention, a polyphase current voltage is applied to the multiplicity of electrodes to effect arc discharge, whereby plasma arcs produced between the electrodes are jetted out from the tips of the electrodes by t

REFERENCES:
patent: 3856915 (1974-12-01), Pagnozzi et al.
patent: 3856918 (1974-12-01), Skrivan et al.
patent: 4073640 (1978-02-01), Soykan
patent: 4518417 (1985-05-01), Lugscheider et al.
patent: 4877448 (1989-10-01), Lindsay
patent: 4883258 (1989-11-01), Foster et al.

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