Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1997-06-10
1999-10-05
Andrews, Melvyn
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
266160, 266172, 266156, C22B 514, C21B 1314
Patent
active
059616903
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for producing molten pig iron or liquid steel pre-products, from particulate iron-oxide-conitaininig material by fluidization, wherein the iron-oxide-containing material is prereduced in at least one prereduction stage by aid of a reducing gas and subsequently is reduced to sponge iron in a final reduction stage, the sponge iron is melted in a meltdown-gasifying zone under the supply of carbon carriers and an oxygen-containing gas, and a CO- and H.sub.2 -containing reducing gas is produced which is introduced into the final reduction stage, is reacted there, is drawn off, subsequently is introduced into at least one prereduction stage, is reacted there, is drawn off, subjected to scrubbing and subsequently is carried off as an export gas and wherein at least a portion of the reacted reducing gas is purified from CO.sub.2, is heated and is used as a recycle-reducing gas for the reduction of the iron-oxide-containing material, and a plant for carrying out the process.
A process of this type is known from U.S. Pat. No. 5,185,032. With this process, in order to utilize the reduction potential and the thermal energy of the reducing gas to the largest possible extent, the reducing gas is conducted through all reduction stages and through preheating stages preceding them in the flow direction of the iron-oxide-containing material, is withdrawn from the first preheating stage as a top gas and subsequently washed, A portion of the top gas is compressed, subjected to CO.sub.2 -elimination and subsequently heated. The top gas thus heated and to a large extent purified from CO.sub.2 subsequently is fed to the reduction process as a recycle-reducing gas, whereby it becomes feasible to exploit the reductants still present within the top gas. One disadvantage involved here is, however, that each of the fluidized-bed reduction stages and each of the preheating stages has to be dimensioned such as to be capable of being operated with the total amount of gas, i.e. freshly produced reducing gas plus recycle-reducing gas.
In the reduction of iron oxides by fluidization utilizing CO/CO.sub.2 mixtures directional, acicular iron precipitations occur on the surface of the fine ore particles at higher temperatures (f.i. in excess of 700.degree. C.) and at a lower reduction potential (i.e. at increased CO.sub.2 and H.sub.2 O contents of the reducing gas). These iron precipitations are at the origin of the "sticking" phenomenon in fluidized beds. With very high degrees of reduction, agglutination of the ore occurs, whereby the reduction process is hampered. If, however, reduction takes place at a very high or at the highest reduction potential of the reducing gas, iron precipitation will be dense or porous, and "sticking" cannot be observed there.
The invention aims at avoiding these disadvantages and difficulties and has as its object to provide a process and a device for carrying out the process which ensure reduction without the occurrence of "sticking", through an increase in the reduction potential of the reducing gas, wherein, however, the amount of carbon carriers utilized for producing the reducing gas is not to be increased; rather, saving of carbon carriers is to be achieved in comparison to the prior art.
In accordance with the invention this object is achieved in that a portion of the reducing gas flowing from the final reduction stage into the prereduction stage is branched off, washed, purified from CO.sub.2 and heated and subsequently is recycled to the final reduction stage.
It is true that with the process according to the invention one renounces exploiting the reduction potential still present within the reducing gas exiting the final reduction stage and branched off from the same for the further reduction stages and/or any preheating stages that may be provided, but it is precisely from this fact that essential advantages result:
In accordance with the invention, a high reduction potential is ensured by increasing the amount of reducing gas, wherein with the reduction process eff
REFERENCES:
patent: 2547685 (1951-04-01), Brassert et al.
patent: 5185032 (1993-02-01), Whipp
patent: 5338336 (1994-08-01), Greenwalt
patent: 5433767 (1995-07-01), Bresser et al.
Kepplinger Werner Leopold
Schenk Johannes-Leopold
Wallner Felix
Andrews Melvyn
Pohang Iron & Steel Co., Ltd
Research Institute of Industrial Science & Technology, Incorpora
Voest-Alpine Industriean-lagenbau GmbH
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