Direct smelting process

Details Direct smelting process Direct smelting process

2000-03-21

2002-11-12

Andrews, Melvyn (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Processes

Producing or treating free metal

C075S501000, C075S502000, C266S225000

Reexamination Certificate

active

06478848

ABSTRACT:

The present invention relates to a process for producing metals (which term includes metal alloys), in particular although by no means exclusively iron, from a metalliferous feed material, such as ores, partly 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 metallurgical feed material.
A 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 bath of molten iron and slag 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 metalliferous feed material to metal in the metal layer.
The term “smelting” is herein understood to mean thermal processing wherein chemical reactions that reduce metal oxides take place to produce liquid metal.
The HIsmelt process also comprises post-combusting reaction gases, such as CO and H
2
, released from the bath in the space above the bath with oxygen-containing gas and transferring the heat 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 is a favourable mass of ascending and thereafter descending droplets or splashes or streams of molten metal and/or slag which 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 pilot plant work on the HIsmelt process and has made a series of significant findings in relation to the process.
One significant finding is that it is possible to achieve a surprisingly high degree of control over the process by:
(a) injecting solid materials, such as metalliferous feed material and solid carbonaceous material, into the metal layer via a plurality of lances/tuyeres positioned above and extending towards the metal layer; and
(b) forming a pipe of a solid material, which typically is at least predominantly slag, on the ends of each lance/tuyere and thereby extending the lengths of the lances/tuyeres.
The control is the result of the lengths of the pipes automatically varying with the level of the molten metal and thereby maintaining a substantially constant spacing between the effective ends of the lances/tuyeres and the metal.
The length of a pipe on a lance/tuyere is determined by the level of molten metal in the molten bath in the vicinity of the lance/tuyere. Specifically, as the molten metal level increases there is a greater likelihood that molten metal that splashes or is otherwise projected from the metal layer will contact and melt the end of a pipe due to the higher heat transfer of metal compared with slag. In addition, as the molten metal level decreases there is less likelihood of contact of molten metal and the pipe and therefore the end of the pipe can progressively increase towards the metal layer. Variations in the molten metal level occur in continuous and batch metal tapping processes and thus the invention is relevant to both types of processes.
In addition to providing a high degree of control over injection of solid materials into the metal layer—which is important in a metal-based direct smelting process such as the HIsmelt process—the present invention makes it possible to operate with fixed solid material injection lances/tuyeres. This is an advantage because movable lances/tuyeres require seals and seals tend to be difficult to design for no leakage or failure.
In addition to the above advantages, the present invention makes it possible to position a lance/tuyere well clear of the splash zone of the molten metal and thereby avoid damage to the lance/tuyere by contact with molten metal, while ensuring that the effective end of the lance/tuyere is as close as possible to the metal layer. This makes it possible to use a water-cooled lance/tuyere without having the lance/tuyere too close to the molten metal to be a serious safety risk. This is a particularly important issue in a molten layer-based smelting process, such as the HIsmelt process. Thus, the present invention makes it possible to reconcile the conflicting requirements of (i) safety, which dictates positioning the lances/tuyeres as far aware as possible from the metal layer and (ii) performance, which dictates positioning the lances/tuyeres close to the metal layer to optimise injection of reactants into the metal layer.
According to the present invention there is provided a direct smelting process for producing metal from a metalliferous feed material which includes the steps of:
(a) forming a molten bath having a metal layer and a slag layer on the metal layer in a metallurgical vessel;
(b) injecting a carrier gas, a metalliferous feed material, and a solid carbonaceous material into the metal layer via a plurality of solid material injection lances/tuyeres positioned above and extending towards the surface of the metal layer and causing molten material to be projected from the molten bath as splashes, droplets and streams into a space above a nominal quiescent surface of the molten bath to form a transition zone;
(c) smelting metalliferous feed material to metal in the metal layer;
(d) injecting an oxygen-containing gas into the vessel via one or more than one lance/tuyere and post-combusting reaction gases released from the molten bath, whereby the ascending and thereafter descending splashes, droplets and streams of molten material in the transition zone facilitate heat transfer to the molten bath, and whereby the transition zone minimises heat loss from the vessel via the side walls in contact with the transition zone; and
the process being characterised by forming a pipe of a solid material on the end of at least one lance/tuyere while injecting the metalliferous feed material and the carbonaceous material through the solid material injection lances/tuyeres and thereby extending the effective length of the lance/tuyere or the lances/tuyeres.
Typically, molten metal is a major part and slag is the remaining part of the molten material in the splashes, droplets, and streams of molten material from the metal layer. Typically, the splashes, droplets, and streams of molten material entrain further molten material (particularly slag) as they move upwardly. In addition, increasingly, the splashes, droplets, and streams of molten material lose momentum and fall downwardly towards the metal layer. In view of the higher density of metal than slag the relative amount of metal in the molten material in the splashes, droplets, and streams decreases with distance from the metal layer to the point where the transition zone may include small amounts, if any, metal.
The term “metal layer” is understood herein to mean that region of the bath that is predominantly metal. Specifically, the term covers a region or zone that includes a dispersion of molten slag in a metal continuous volume.
The term “slag layer” is understood herein to mean that region of the bath that is predominantly slag. Specifically, the term covers a region or zone that includes a dispersion of molten metal in a slag continuous volume.
The space above the nominal quiescent surface of the bath is hereinafter referred to as the “top space”.
The term “quiescent surface” in the context of the molten bath is understood to mean the surface of the molten bath under process conditions in which there is no gas/solids injection and therefore no bath agitation.
Similarly, the term “quiescent surface” in the context of the metal lay

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