Direct smelting process

Details Direct smelting process Direct smelting process

2000-03-21

2002-06-11

Andrews, Melvyn (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Processes

Producing or treating free metal

C075S501000, C075S502000

Reexamination Certificate

active

06402808

ABSTRACT:

The present invention relates to a process and to an apparatus for producing molten metal (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 metalliferous feed material.
A process that produces molten metal directly from a metalliferous feed material is generally referred to as a “direct smelting process”.
One 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 is 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 with 3 regions, namely: an upper region for post-combusting reaction gases with injected oxygen; a lower region for smelting metal oxides to metal; and an intermediate region which separates the upper and lower regions. 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 Interational application PCT/AU96/00197 (WO 96/31627 published on Oct. 10, 1996, and corresponding to U.S. Pat. No. 6,083,296) 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 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 material.
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/or slag which provide an effective medium to transfer to the bath the thermal energy generated by post-combusting reaction gases above the bath.
An object of the present invention is to provide a direct smelting process and apparatus that can be used with a wide range of coal types, including low grade coals.
According to the present invention there is provided a process for direct smelting a metalliferous feed material which includes the steps of:
(a) pre-treating coal with an oxygen-containing gas and producing char and a fuel gas;
(b) heating an oxygen-containing gas and/or producing an oxygen-containing gas in an oxygen plant using at least part of the fuel gas produced in step (a) as a source of energy;
(c) injecting the metalliferous feed material, char produced in step (a), and the oxygen-containing gas heated or produced in step (b) into a direct smelting vessel; and
(d) direct smelting the metalliferous feed material to molten metal in the direct smelting vessel using the char as a source of energy and as a reductant and post-combusting reaction gas produced in the smelting process with the oxygen-containing gas.
An advantage of the process of the present invention is that pre-treatment step (a) changes the properties/composition of coal and makes it more suitable for direct smelting metalliferous feed material. As a consequence, the process can operate with low grade coal at high productivity in terms of molten metal produced in the direct smelting vessel. The term “low grade coal” means coal which has low heating values and high levels of impurities relative to normal steaming coals and can be upgraded. The term “impurities” means impurities such as sulphur, alkali, salts, and volatiles. These impurities partition between the char and the fuel gas in pre-treatment step (a). As a consequence, pre-treatment step (a) results in reduced loadings of the impurities supplied to the direct smelting vessel. The reduced impurity loadings are an advantage because they mean that the rate of smelting metalliferous feed material can be increased and the volumes of off-gas discharged from the vessel can be decreased. Both outcomes are an advantage.
Moreover, the process of the present invention includes the advantageous option of using fuel gas that is produced in step (a) to heat an oxygen-containing gas, preferably air or oxygen-enriched air, which in turn is used in the direct smelting vessel. In direct smelting processes which can operate with heated air or oxygen-enriched air to post-combust reaction gases, such as the HIsmelt process, the task of generating the heated air and oxygen-enriched air is a significant issue. The fuel gas produced in step (a) is well-suited as a source of energy for heating air, for example in hot blast stoves, and therefore is a significant advantage of the process of the present invention on this basis.
The term “metalliferous feed material” is understood herein to mean any metal feed material which includes metal oxides, such as ores, partly reduced ores, and metal-containing waste streams.
The term “char” is understood herein to mean a solid product remaining after at least 50% of the moisture/bound oxygen/volatiles have been removed from coal.
Preferably, step (b) includes supplying the fuel gas to a hot air blast means and using the fuel gas as a source of energy for heating air in the hot air blast means.
Preferably the hot air blast means are hot blast stoves.
Preferably the process includes preheating the metalliferous feed material using a part of the fuel gas produced in step (a) prior to injecting the feed material into the direct smelting vessel.
Depending on the composition, the fuel gas may also be used to partially reduce the metalliferous feed material prior to injecting the feed material into the direct smelting vessel.
Step (d) may include any suitable direct smelting process.
Preferably step (d) includes direct smelting the metalliferous feed material in accordance with the HIsmelt process which includes:
(a) forming a molten bath having a metal layer and a slag layer on the metal layer in the direct smelting vessel;
(b) injecting the metalliferous feed material and the char into the metal layer via a plurality of lances/tuyeres;
(c) smelting the metalliferous feed material to molten metal substantially in the metal layer;
(d) causing molten metal and slag to be projected as splashes, droplets, and streams into a space above a nominal quiescent surface of the molten bath and forming a transition zone; and
(e) injecting the oxygen-containing gas into the direct smelting 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 metal and slag 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 wall in contact with the

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