Specialized metallurgical processes – compositions for use therei – Processes – Electrothermic processes
Patent
1999-02-12
2000-11-14
King, Roy V.
Specialized metallurgical processes, compositions for use therei
Processes
Electrothermic processes
75 1015, 75 1018, 75 1062, 75 1063, 75560, 75569, 373161, C21B 1100, C21C 700, C22B 400
Patent
active
061464376
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a metal containing compound reduction and melting process of the type which entails feeding a burden comprising a mixture of the metal containing compound and a suitable reductant in particulate form into the heating vessel of a channel type induction furnace which contains a bath of the said metal in liquid form so that at least one heap of burden forms above the metal bath.
Such process is known from U.S. Pat. No. 5,411,570.
Most conventional metal containing compound reduction processes involve the heating of the metal containing compound (usually the metal oxide) in the presence of a reductant such as a suitable carbon containing compound or the like. The metal containing compound and reductant are usually collectively referred to as the burden.
In the aforesaid conventional processes, the rate at which such heating takes place is usually so rapid that at least a substantial part of the burden is melted before the reduction reactions are completed. A substantial amount of the reduction accordingly takes place in the liquid phase.
On such melting of the burden, a slag is formed which, apart from the oxides of the said metal containing compound, also contains the oxides of other metals which may be present in the burden.
In order to recover the said metal containing compound from its oxide in the slag, a further amount of the reductant is required in the reaction which can accordingly give rise to a metal product with an unwanted high carbon content.
Such high carbon in the product is usually subsequently reduced by oxidation, either by adding to the product oxygen as gaseous oxygen or air, or by utilising a suitable metal oxide present in the reaction medium. Such oxidation reaction accordingly also takes place in the liquid phase.
It will be appreciated that apart from requiring an initial excess of reductant, the subsequent oxidation of such excess entails a further step in the process.
As a result of both the aforesaid reduction and oxidation reactions, relatively large volumes of unwanted gas are formed below the surface of the liquid metal and slag which then escape in the form of bubbles from the liquid metal and slag.
In above-mentioned U.S. Pat. No. 5,411,570 a steel making process is disclosed in which the burden is added to the furnace in two heaps which remain separated from each other by a slag layer, floating on top of the liquid metal bath. In this arrangement it is possible for the burden to pass directly into the metal bath or any slag which may be present, so that at least part of the reduction of the burden takes place in the liquid phase, which not only gives rise to unwanted gas formation in the furnace but also to a potential loss of product.
It is accordingly an object of this invention to provide a metal reduction and melting process with which the aforesaid problems can be overcome or at least minimised.
According to the invention this object is achieved by a process of the type described, in which the burden is fed into the vessel in such a manner and rate that it forms a continuous layer of burden which extends in the manner of a bridge over the whole of the liquid bath and any slag which may be present, with the result that a reaction zone is formed in the burden in which all the metal containing compound can be reduced, and a melting zone is formed below the metal reduction zone in which all the reduced metal can be melted; and controlling such process in such a manner that said continuous layer is maintained during substantially the whole duration of the process, and so that all the reduction of the metal containing compound takes place in the solid phase.
It will be appreciated that because substantially no liquid phase reactions take place during the process according to the invention, the aforesaid unwanted gas evolution is practically eliminated, and in practice the substantial absence of bubble formation in the liquid metal bath and slag which is formed is used as an indication that the process is being controlled correctly.
It will be apprecia
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The American Heritage Dictionary of the English Language, Third Edition 1992. Houghton Mifflin Company.
Harten, K.P., et al., "Umschau", Stahl Und Eisen, 74(5), 291-302, (Feb. 1954).
Ipcor NV
King Roy V.
McGuthry-Banks Tima
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