Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Patent
1997-01-15
1999-02-16
Andrews, Melvyn
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
75450, 266 78, 266156, 266172, C21B 1300
Patent
active
058715606
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a process for the direct reduction of iron-oxide-containing material, wherein synthesis gas, preferably reformed natural gas, is mixed with top gas forming in the direct reduction of the iron-oxide-containing material and is used as a reducing gas for direct reduction and for heating the iron-oxide-containing material to reduction temperature, as well as a plant for carrying out the process.
DESCRIPTION OF THE RELATED ART
A process of this type is known from EP-A-0 571 358.
Metallic plant parts that get into contact with CO-containing reducing gas are subject to a high stress due to corrosion: The result 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 reducing gas, thus, being particularly jeopardized. With a plant for carrying out the initially mentioned process, these are primarily the reactors employed for direct reduction and the gas heaters 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 an 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, which enables the adjustment of the content of H.sub.2 S to a predetermined value with sufficient accuracy and by avoiding great procedural and structural expenditures as well as high costs.
In accordance with the invention, this object is achieved in that at least a portion of the sulfur contained in the iron-oxide-containing material, together with the top gas, is fed to the reducing gas in the form of H.sub.2 S incurring in heating and in direct reduction, respectively.
The invention is based on the idea to utilize the sulfur usually contained in the ore and which has not been used in further processing so far, taking advantage of the fact that H.sub.2 S is formed when heating sulfide ores. According to the invention, this H.sub.2 S, together with the reducing gas effecting heating and by which it is absorbed, is carried off as a top gas and fed to the reducing gas.
Suitably, a content of H.sub.2 S ranging from 20 to 40 ppmV, preferably amounting to about 25 ppmV, is adjusted in the reducing gas by means of the top gas.
According to a preferred embodiment, the top gas is subjected to CO.sub.2 scrubbing prior to being used as a reducing gas and the adjustment of the H.sub.2 S content in the reducing gas is effected by directly admixing to the reducing gas at least a partial volume of the top gas while avoiding CO.sub.2 scrubbing. This variant is particularly simple to realize, because the only thing to be provided is a bypass duct bypassing the CO.sub.2 scrubber. Thereby, washing out of the H.sub.2 S present in that portion of the top gas is prevented, whereas the remaining portion of the top gas is subjected to CO.sub.2 scrubbing, by which also H.sub.2 S is washed out. By varying the amount of top gas conducted through the bypass duct, the desired H.sub.2 S content of the reducing gas may be adjusted in a simple manner.
Another preferred embodiment is characterized in that reformed natural gas is employed as the synthesis gas and that both the reformed natural gas and the top gas are subjected to CO.sub.2 scrubbing prior to being used as a reducing gas, wherein a partial volume of the reformed natural gas is directly admixed to the reducing gas while avoiding CO.sub.2 scrubbing. Thereby, any desired CO.s
REFERENCES:
patent: 3936296 (1976-02-01), Campbell
patent: 4333761 (1982-06-01), Ahrendt et al.
patent: 4376648 (1983-03-01), Ohtawa et al.
patent: 5531424 (1996-07-01), Whipp
Czermak Karl
Fluch Roland
Peer Gunter
Whipp, Jr. Roy Hubert
Andrews Melvyn
Brifer International Ltd.
Voest-Alpine Industriean-lagenbau GmbH
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