Metallurgical apparatus – Means for melting or vaporizing metal or treating liquefied... – By means introducing treating material
Reexamination Certificate
2002-10-03
2003-07-22
Andrews, Melvyn (Department: 1742)
Metallurgical apparatus
Means for melting or vaporizing metal or treating liquefied...
By means introducing treating material
C266S270000
Reexamination Certificate
active
06596223
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process and an apparatus for producing iron and/or ferroalloys from ferruginous material, including iron ores, other ores containing iron such as chromite ores, partially reduced ores, and iron-containing waste streams such as steel reverts.
The present invention relates particularly to a molten metal bath-based direct smelting process and an apparatus for producing molten iron and/or ferroalloys.
2. Description of Related Art
One known molten bath-based direct smelting process for producing molten iron is the DIOS process. The DIOS process includes a pre-reduction stage and a smelt reduction stage. In the DIOS process ore (−8 mm) is pre-heated (750° C.) and pre-reduced (10 to 30%) in bubbling fluidised beds using offgas from a smelt reduction vessel which contains a molten bath of iron and slag, with the slag forming a deep layer on the iron. The fine (−0.3 mm) and coarse (−8 mm) components of the ore are separated in the pre-reduction stage of the process and the −0.3 mm component is collected in a cyclone and injected into the smelt reduction vessel with nitrogen whilst the coarse ore is charged by gravity. Pre-dried coal is charged directly to the smelt reduction vessel from the top of the vessel. The coal decomposes into char and volatile matter in the slag layer and the ore dissolves in the molten slag and forms FeO. The FeO is reduced at the slag/iron and slag/char interfaces to produce iron. The carbon monoxide generated at the iron/slag and slag/char interfaces generates a foaming slag. Oxygen is blown through a specially designed lance that introduces the oxygen inside the foamed slag and improves secondary combustion. Oxygen jets burn carbon monoxide that is generated with the smelting reduction reactions, thereby generating heat that is transferred first to the molten slag and then to the slag/iron interface by the strong stirring effect of bottom blowing gas. The stirring gas introduced into the hot iron bath from the bottom or side of the smelt reduction vessel improves heat transfer efficiency and increases the slag/iron interface for reduction and therefore the vessel productivity and thermal efficiency. However, injection rates must be limited as strong stirring lowers secondary combustion due to increased interaction between the oxygen jet and iron droplets in the slag with subsequent lowering of productivity and increased refractory wear. Slag and iron are tapped periodically.
Another known direct smelting process for producing molten iron is the Romelt process. The Romelt process is based on the use of a large volume, highly agitated slag bath as the medium for smelting ferruginous feed material to iron in a smelt reduction vessel and for post-combusting gaseous reaction products and transferring the heat as required to continue smelting ferruginous feed material. The ferruginous feed material, coal, and fluxes are gravity fed into the slag bath via an opening in the roof of the vessel. The Romelt process includes injecting a primary blast of oxygen-enriched air into the slag via a lower row of tuyeres to cause necessary slag agitation and injection of oxygen-enriched air or oxygen into the slag via an upper row of tuyeres to promote post-combustion. The molten iron produced in the slag moves downwardly and forms an iron layer and is discharged via a forehearth. In the Romelt process the iron layer is not an important reaction medium.
Another known direct smelting process for producing molten iron is the AISI process. The AISI process includes a pre-reduction stage and a smelt reduction stage. In the AISI process pre-heated and partially pre-reduced iron ore pellets, coal or coke breeze and fluxes are top charged into a pressurised smelt reactor which contains a molten bath of iron and slag. The coal devolatilises in the slag layer and the iron ore pellets dissolve in the slag and then are reduced by carbon (char) in the slag. The process conditions result in slag foaming. Carbon monoxide and hydrogen generated in the process are post combusted in or just above the slag layer to provide the energy required for the endothermic reduction reactions. Oxygen is top blown through a central, water cooled lance and nitrogen is injected through tuyeres at the bottom of the reactor to ensure sufficient stirring to facilitate heat transfer of the post combustion energy to the bath. The process offgas is de-dusted in a hot cyclone before being fed to a shaft type furnace for pre-heating and pre-reduction of the pellets to FeO or wustite.
Another known direct smelting process, which relies on a molten iron layer as a reaction medium, and is generally referred to as the HIsmelt process, is described in International application PCT/AU96/00197 (WO 96/31627) in the name of the applicant.
The HIsmelt process as described in the International application includes:
(a) forming a bath of molten iron and slag in a vessel;
(b) injecting into the bath:
(i) ferruginous feed material, typically iron oxides; and
(ii) a solid carbonaceous material, typically coal, which acts as a reductant of the iron oxides and a source of energy; and
(c) smelting the metalliferous feed material to metal in the iron layer.
The HIsmelt process also includes injecting oxygen-containing gas into a space above the bath and post-combusting reaction gases, such as CO and H
2
, released from the bath and transferring the heat generated to the bath to contribute to the thermal energy required to smelt the metalliferous feed materials.
The HIsmelt process also includes forming a transition zone in the space above the nominal quiescent surface of the bath in which there is a favourable mass of ascending and thereafter descending droplets or splashes or streams of molten material that provide an effective medium to transfer to the bath the thermal energy generated by post-combusting reaction gases above the bath.
The applicant has carried out extensive research and development work on direct smelting processes including research and development work on the requirements for commercially operating processes and has made a series of significant findings in relation to such processes.
The focus of the present invention is on post combustion of reaction gases.
Without adequate post combustion of reaction gases and subsequent transfer of heat back to the molten bath, such molten bath based direct smelting processes, particularly those without a pre-reduction stage, become uneconomic and in many cases unworkable because of the endothermic nature of the reduction of ferruginous materials.
A further issue is that good post combustion must not be at the expense of re-oxidising significant amounts of molten metal in the molten bath as the process becomes inefficient, with excessive amounts of solid carbonaceous material being needed to counter such oxidation.
As well, excessively high amounts of liquid FeO in the molten bath are particularly detrimental to refractory wear around the region of the nominal quiescent level of the molten metal.
SUMMARY OF THE INVENTION
In general terms, the present invention is a direct smelting process for producing iron and/or ferroalloys which operates on a commercial scale in a metallurgical vessel that has a hearth, side walls, and a roof, and a minimum width dimension of the interior of the hearth of at least 4 meters, more preferably at least 6 meters.
In more specific terms, the direct smelting process includes the steps of:
(a) forming a molten bath containing molten metal and molten slag;
(b) supplying feed materials being ferruginous material, carbonaceous material, and fluxes into the vessel;
(c) smelting ferruginous feed material to molten metal in the molten bath and generating gases in the bath;
(d) injecting oxygen-containing gas being air or air with up to 50% oxygen into a space above the quiescent surface of the molten bath (the “top space”) and combusting gases generated in the process; and
(e) generating upward movement of molten material from the molten bath
Andrews Melvyn
Kerins John C.
Miles & Stockbridge P.C.
Technological Resources Pty. Ltd.
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