Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1997-01-15
1999-01-12
Andrews, Melvyn
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75450, 266 78, 266156, 266172, C21B 1300
Patent
active
058580581
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a process for avoiding metal dusting in the direct reduction of iron-oxide-containing material, wherein synthesis gas is mixed with top gas forming in the direct reduction of the iron-containing material and is used as a CO- and H.sub.2 -containing reducing gas for the direct reduction of the iron-oxide-containing material, as well as a plant for carrying out the process.
DESCRIPTION OF THE RELATED ART
A process of this type is known, for instance, from U.S. Pat. No. 2,752,234, U.S. Pat. No. 5,082,251 and EP-A - 0 571 358.
From EP-A - 0 571 358 it is known to carry out the reduction of fine ore not exclusively via the strongly endothermic reaction with H.sub.2 according to lower the operational costs, in particular the energy costs, involved.
However, in metallic plant parts that get into contact with CO-containing reducing gas are subject to a high stress due to corrosion: The result, i.a., is metal decomposition, which is denoted as "metal dusting" in the technical literature. Metal dusting occurs to an increased extent at elevated temperatures, plant parts that get into contact with hot CO-containing reducing gas, thus, being particularly jeopardized. With a plant for carrying out the initially mentioned process, these are the reactors employed for direct reduction and the gas heater heating the reducing gas to reduction temperature.
To avoid or reduce metal dusting, it is internally known to provide for a content of sulfur within the reducing gas, which has been accomplished by blowing in H.sub.2 S gas through tuyeres. Such an admixture of H.sub.2 S gas is not only technologically complex, but also very expensive and, in addition, involves procedural difficulties, i.e., it is difficult to adjust the H.sub.2 S content in the reducing gas uniformly to a predetermined value as a function of the chemical composition of the reducing gas.
SUMMARY OF THE INVENTION
The invention aims at avoiding these disadvantages and difficulties and has as its object to provide a process of the initially defined kind, and a plant for carrying out the process, by which the occurrence of metal dusting is minimized or prevented in a simple manner despite an elevated Co content of the reducing gas, in particular, in a procedurally and structurally simple and cost-saving manner, so that the service life of metallic plant parts will be considerably increased.
In a process of the initially described kind, this object is achieved in that the reducing gas is adjusted to a predetermined per se known CO/CO.sub.2 ratio of between 1 and 3, namely by adjusting the operating characteristics of a reformer that serves for the production of synthesis gas from natural gas by reformation, by varying the vapor
atural-gas ratio during feeding of the reformer.
By adjusting a CO/CO.sub.2 ratio of between 1 and 3 it is feasible to decisively lower the reaction activity of the CO contained in the reducing gas relative to metal, in particular steel, and hence the need for repair work of the direct reduction plant, without having to renounce elevated CO contents enabling the procedurally beneficial exothermic reaction with Fe.sub.2 O.sub.3.
From DE-A 2 103 731, a process is known for directly reducing lumpy or agglomerated iron-ore-containing materials in a shaft furnace by hydrogen-containing reducing gases at elevated pressure, wherein reduction is effected employing hydrogen as the reducing gas containing impurities in an amount of maximally 5 Vol. % CO, 5 Vol. % CO.sub.2, 5 Vol. % CH.sub.2 and 2 Vol. % water vapor. Herein, the hydrogen-containing reducing gas, which contains roughly 90 Vol. % H.sub.2, can contain 1.9 Vol. % CO.sub.2 and 4.1 Vol. % CO. CO and CO.sub.2 are here merely impurities.
According to a variant of the process according to the invention, the adjustment of the CO/CO.sub.2 ratio is effected in that a partial volume of the reformed gas, which is produced from vapor and natural gas in a reformer and subsequently is fed to CO conversion to increase its H.sub.2 content, is adm
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patent: 5082251 (1992-01-01), Whipp
patent: 5213611 (1993-05-01), Carranza-Almaguer
patent: 5382277 (1995-01-01), Rose
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Kepplinger Werner Leopold
Kern Gerald
Schenk Johannes
Whipp, Jr. Roy Hubert
Andrews Melvyn
Brifer International Ltd.
Voest-Alpine Industriean-lagenbau GmbH
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