Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1993-10-27
1995-12-05
Andrews, Melvyn
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75501, 75502, 75707, 266173, 266182, 266186, C21B 1106
Patent
active
054724783
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of reducing metal oxides, in particular iron ore, and to a vessel for use in the method.
There are two methods of reducing iron ore which have obtained particular significance.
In the first method iron ore, preferably pre-heated and pre-reduced, and coal are injected into or onto an iron bath in a vessel. The coal is dissolved in the iron bath and the iron ore is reduced to molten iron. The method includes injecting an oxygen-containing gas into the gas space above the iron bath to post-combust CO and H.sub.2 from the iron bath so that a considerable portion of the energy released is transferred to the iron bath. In a preferred form of the method coal and oxygen-containing gas are injected into the iron bath through bottom tuyeres and cause droplets/streams of molten metal and slag to be ejected upwardly into the gas space to provide a medium for transferring efficiently the energy released by the post-combustion of CO and H.sub.2. However, whilst the method has the advantage of efficient energy transfer to the iron bath to balance the heat loss from the iron bath due to the endothermic reduction of iron ore, a disadvantage of the method is that a proportion of the molten iron ejected into the gas space is oxidized and must be re-reduced in the iron bath.
In the second method the undesirable oxidation of molten iron is avoided by separating the molten iron from the gas space by a relatively deep slag layer and reducing the rate of bottom blowing. Thus, there is a minimal contact between the molten iron and the gas space. The major disadvantage of the method is that it is difficult to transfer efficiently energy released by post-combustion in the gas space to the iron bath. A further disadvantage is that the poor energy transfer results in high waste gas temperatures which cause accelerated wear of refractory linings in the vessel.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a method of reducing iron ore which alleviates the disadvantages of the known methods described in the preceding paragraphs.
According to the present invention there is provided a method of reducing metal oxides in a vessel containing a molten bath, the bath comprising a metal layer and a slag layer, the method comprising:
The term "metal layer" as used herein is understood to mean a layer that predominantly comprises metal.
The term "slag layer" as used herein is understood to mean a layer that predominantly comprises slag.
In effect, the slag layer separates the metal layer and the gas space above the bath so that oxidation of CO and any H.sub.2 in the gas space does not interfere with reduction of metal oxides in the metal layer and vice versa, and the injection of gas directly into the slag layer makes possible efficient transfer of heat generated by the post-combustion of CO and any H.sub.2 in the gas space to the slag layer and subsequently to the metal layer to balance the heat loss in the reduction of metal oxides.
It is preferred that metal oxides and carbonaceous material are each injected into and onto the bath.
It is preferred that the carbonaceous material be selected from one or more of the group comprising coal, spent pot linings from aluminium smelting furnaces, and sewage sludge. It is particularly preferred that the carbonaceous material comprises coal.
It is preferred that the gas injected into the slag layer be selected from one or more of an inert gas, recycled process gas, CO, CO.sub.2, natural gas, propane, or butane. It is particularly preferred that the inert gas be nitrogen.
According to a preferred embodiment of the present invention the outlet openings of the means for injecting a gas into the slag layer are arranged below the bath surface of the slag layer in a distance from the side wall of the vessel. It is advantageous not to introduce the gas stream into the slag layer right at the side wall of the vessel as it is in the case with side wall tuyeres in a converter-like vessel but in a distance from the side wall. For the formation
REFERENCES:
patent: 3542352 (1970-11-01), Themelis et al.
patent: 4798624 (1989-01-01), Brotzmann et al.
patent: 4936908 (1990-06-01), Takahashi et al.
patent: 5051127 (1991-09-01), Hardie et al.
Andrews Melvyn
Technological Resources Pty. Ltd.
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