Direct smelting process

Details Direct smelting process Direct smelting process

2000-09-26

2002-08-06

King, Roy (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Processes

Producing or treating free metal

C075S538000, C075S548000

Reexamination Certificate

active

06428603

ABSTRACT:

The present invention relates to a process for producing molten metal (which term includes metal alloys), in particular although by no means exclusively iron, from metalliferous feed material, such as ores, partially reduced ores and metal-containing waste streams, in a metallurgical vessel containing a molten bath.
The present invention relates particularly to a molten metal bath-based direct smelting process for producing molten metal from a metalliferous feed material.
The most widely used process for producing molten iron is based on the use of a blast furnace. Solid material is charged into the top of the furnace and molten iron is tapped from the hearth. The solid material includes iron ore (in sinter, lump or pellet form), coke, and fluxes and forms a permeable burden that moves downwardly. Preheated air, which may be oxygen enriched, is injected into the bottom of the furnace and moves upwardly through the permeable bed and generates carbon monoxide and heat by combustion of coke. The result of these reactions is to produce molten iron and slag.
A process that produces iron by reduction of iron ore below the melting point of the iron produced is generally classified as a “direct reduction process” and the product is referred to as DRI.
The FIOR (Fluid Iron Ore Reduction) process is an example of direct reduction process. The process reduces iron ore fines as the fines are gravity-fed through each reactor in a series of fluid bed reactors. The fines are reduced in solid state by compressed reducing gas that enters the bottom of the lowest reactor in the series and flows counter-current to the downward movement of fines.
Other direct reduction processes include moving shaft furnace-based processes, static shaft furnace-based processes, rotary hearth-based processes, rotary kiln-based processes, and retort-based processes.
The COREX process includes a direct reduction process as one stage. The COREX process produces molten iron directly from coal without the blast furnace requirement of coke. The COREX process includes 2-stage operation in which:
(a) DRI is produced in a shaft furnace from a permeable bed of iron ore (in lump or pellet form) and fluxes; and
(b) the DRI is then charged without cooling into a connected melter gasifier and melted.
Partial combustion of coal in the fluidised bed of the melter gasifier produces reducing gas for the shaft furnace.
Another known group of processes for producing iron is based on cyclone converters in which iron ore is melted by combustion of oxygen and reducing gas in an upper melting cyclone and is smelted in a lower smelter containing a bath of molten iron. The lower smelter generates the reducing gas for the upper melting cyclone.
A process that produces molten metal directly from ores (and partially reduced ores) is generally referred to as a “direct smelting process”.
One known group of direct smelting processes is based on the use of electric furnaces as the major source of energy for the smelting reactions.
Another known direct smelting process, which is generally referred to as the Romelt process, is based on the use of a large volume, highly agitated slag bath as the medium for smelting top-charged metal oxides to metal and for post-combusting gaseous reaction products and transferring the heat as required to continue smelting metal oxides. The Romelt process includes injection of oxygen enriched air or oxygen into the slag via a lower row of tuyeres to provide slag agitation and injection of oxygen into the slag via an upper row of tuyeres to promote post-combustion in the Romelt process the metal layer is not an important reaction medium.
Another known group of direct smelting processes that are slag-based is generally described as “deep slag” processes. These processes, such as DIOS and AISI processes, are based on forming a deep layer of slag. As with the Romelt process, the metal layer below the slag layer is not an important reaction medium.
Another known direct smelting process which relies on a molten metal 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 comprises:
(a) forming a molten bath having a metal layer and a slag layer on the metal layer in a vessel;
(b) injecting into the bath:
(i) a metalliferous feed material, typically metal oxides; and
(ii) a solid carbonaceous material, typically coal, which acts as a reductant of the metal oxides and a source of energy; and,
(c) smelting the metalliferous feed material to metal in the metal layer.
The HIsmelt process also comprises post-combusting reaction gases, such as CO and H
2
, released from the bath in the apace above the bath with oxygen-containing gas and transferring the beat generated by the post-combustion to the bath to contribute to the thermal energy required to smelt the metalliferous feed materials.
The HIsmelt process also comprises forming a transition zone above the nominal quiescent surface of the bath in which there are ascending and thereafter descending droplets or splashes or streams of molten metal and slag which provide an effective medium to transfer to the bath the thermal energy generated by post-combusting reaction gases above the bath.
A preferred form of the HIsmelt process is characterized by forming the transition zone by injecting carrier gas, metalliferous feed material, solid carbonaceous material and optionally fluxes into the bath through lances that extend downwardly and inwardly through side walls of the vessel so that the carrier gas and the solid material penetrate the metal layer and cause molten material to be projected from the bath.
This form of the HIsmelt process is an improvement over earlier forms of the process which form the transition zone by bottom injection of carrier gas and solid carbonaceous material through tuyeres into the bath which causes droplets, splashes and streams of molten material to be projected from the bath.
The applicant has carried out extensive pilot plant work on the above-described preferred form of the HIsmelt process and has made a series of significant findings in relation to the process.
One of the findings made by the applicant, which forms the basis of the present invention, is that the upward flow rate of bath-derived gas caused by the injection of solid material/carrier gas into the molten bath should be at least 0.30 Nm
3
/s/m
2
at the location of the interface of the metal layer and the slag layer (under quiescent conditions) to establish the transition zone so that there is heat transfer to the molten bath at an effective rate.
Heat transfer efficiency is a measure of the amount of the available energy generated by post combustion that is transferred to the molten bath. It is also a measure of the amount of the available energy generated by post combustion that is lost from the vessel (via discharge of off-gas above bath temperature and heat transfer via the side walls and roof of the vessel).
The minimum bath-derived gas flow rate of 0.30 Nm
3
/s/m
2
at the interface of the metal layer and the slag layer (under quiescent conditions) ensures that there is sufficient buoyancy uplift of splashes, droplets and streams of molten material from the molten bath into the transition zone to maximise:
(a) heat transfer to the molten bath via subsequently descending splashes, droplets and streams of molten material; and
(b) contact of molten material with the side walls of the vessel which forms a protective layer of slag that reduces heat loss from the vessel.
Item (b) above is a particularly important consideration in the context of the preferred vessel construction of the present invention which includes water cooled panels that form the side walls in the upper barrel section and optionally the roof and water cooled refractory bricks that Form the side walls in the lower barrel section of the vessel.
In general terms, the present invention is a direct smelting process for producing me

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