Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
1998-12-29
2001-05-22
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C266S156000
Reexamination Certificate
active
06235083
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a hot CO- and H
2
-containing reducing gas serving for the reduction of lumpy metal ore, in particular iron ore, wherein the reducing gas is formed in a gasification zone by the gasification of carbon carriers, in particular coal, taking place under a supply of oxygen and subsequently cooled down to a reducing-gas temperature favorable to the reduction process, and a plant for carrying out the method.
A method of the initially described kind is known i.e., from DE-C - 30 34539 and from EP-B 0 114 040. With these known methods, pig iron or a steel pre-product are produced by smelting from at least prereduced sponge iron in a meltdown gasifying zone under the supply of carbon carriers and oxygen-containing gas, and a CO- and H,-containing reducing gas is generated. The reducing gas formed in the meltdown gasifying z one exhibits a temperature in the range of 1000 to 1200° C. At this temperature, the released hydrocarbon compounds are decomposed. At the same time, the CO
2
and H
2
O contents drop to below 6% CO
2
and 4% H
2
O on account of these temperatures, since they are converted to CO and H
2
.
For utilization in a reduction reactor, this very hot reducing gas has to be cooled prior to introduction into the reduction reactor. In accordance with DE-C - 30 34 539 fi., a spray cooler with a subsequently connected scrubbing tower is provided to that end. The portion of the reducing gas thus cooled is admixed with the reducing gas exiting the melt-down gasifying zone. Such routinely effected cooling of the reducing gas by cooled reducing gas of the same type to roughly 700 to 900° C prevents the occurrence of incipient melting of the ore particles in the reduction zone during ore reduction, but without causing a decrease in the reduction potential of the reducing gas.
Yet it is disadvantageous that the reducing gas thus cooled is thermodynamically unstable; from the carbon monoxide, carbon dioxide and carbon form in accordance with the Boudouard equilibrium, just as in accordance with the heterogeneous water-gas equilibrium a reaction of carbon monoxide with hydrogen to water and carbon takes place, which reaction is also exothermnic, like the reaction described first. This leads to an increase in temperature of the reducing gas and hence to an increase in temperature of the shaft material. There will tie the formation of agglomerates. Thus not only is the reduction process affected but the yield of shaft material from the reduction zone is affected as well.
The present invention aims at avoiding these disadvantages and difficulties and has as its object to provide a method of the initially described kind and a plant for carrying out the method, enabling a reducing gas to be produced having a temperature range that is favorable to the reduction of the metal ore, hence lying below the temperature at which instances of incipient melting and fouling (formation of agglomerates) may occur in the at least partially reduced metal ore. Moreover, a chemical attack on the metallic materials of the gas-carrying systems, that is, reactors and gas conveying ducts, built-in structures etc., is to be avoided.
SUMMARY OF THE INVENTION
With a method of the initially described kind, this object is achieved in that the reducing gas, by the addition of H
2
O and/or CO
2
, prevents the Boudouard and heterogeneous water-gas reaction and the resultant heating of the reducing gas and thus the metal oreis converted to a reducing gas that is thermodynamically more stable at the reducing-gas temperature.
By selectively adding H
2
O and/ or CO
2
, the thermodynically conditioned decomposition of the reductants CO and H
2
is selectively influenced or prevented. In the reducing gas, ranges of concentration are adjusted at which the Boudouard and heterogeneous water-gas reaction, which is strongly exothermic, is suppressed, so that an interfering temperature increase in the reducing gas cannot take place. At the same time, the degree of oxidation of the reducing gas is controlled and the chemical attack on metallic materials is suppressed
Advantageously, amounts of H
2
O and/or CO
2
are added until the Boudouard and heterogeneous water-gas equilibrim of the reducing gas at the temperature favorable to the reduction process is almost attained. Preferably, cooling of the reducing gas can be effected by feeding cooling gas of the same type, i.e., top gas and/or H
2
O and/or CO
2
.
Suitably, the addition of H
2
O is effected by feeding water vapor and the addition of CO
2
is effected by feeding a CO
2
-containing gas. In accordance with a preferred embodiment, feeding of CO
2
into the reducing gas can at least partially be effected in that a reducing gas reacted in a reduction process of the metal ore, socalled top gas, is fed into the reducing gas. Other CO
2
-containing gases, i.e., from a CO
2
-purification, may also be employed.
To attain intensive cooling of the reducing gas, cooled reducing gas of the same type is advantageously admixed to the reducing gas, as is known per se from the prior art, and H
2
O and/or CO
2
are added into the cooled reducing gas and/or into the hot reducing gas coming from the gasification reactor.
A plant for carrying out the method, comprising at least one reduction reactor having a conveying duct for metal ore and a reducing-gas duct running into it and comprising a gasification reactor having feed ducts for carbon carriers and oxygen-containing gases running into it and the reducing-gas duct departing from it is characterized in that a CO
2
source and/or H
2
O source is (are) flow-connected with the reducing-gas duct. Advantageously, the reduction reactor is provided with a top-gas discharge duct carrying off reacted reducing gas from which a branch duct departs that is flow-connected with the reducing-gas duct. Another preferred embodiment is characterized in that from the reducing-gas duct a reducinggas recycle duct via a scrubber and a compressor runs into the reducing-gas duct again, but viewed in the gas flow direction at a position upstream of the branching-off point of the reducing-gas recycle duct, particularly upstream of the position of a dedustification means provided in the reducing-gas duct, and that a CO
2
source and/or H
2
O source is connected with the reducing-gas recycle duct.
REFERENCES:
patent: 5185032 (1993-02-01), Whipp
patent: 5259864 (1993-11-01), Greenwalt
patent: 3034539 (1982-03-01), None
patent: 0122239 (1984-10-01), None
patent: 0179734 (1986-04-01), None
patent: 0114040 (1986-07-01), None
patent: 766167 (1933-12-01), None
patent: 2236951 (1974-05-01), None
patent: 2272177 (1975-03-01), None
Patent Abstract of Japan of Publication No. 58058206, Jun. 4, 1983.
Brunnbauer Günther
Kastner Walter Rainer
Kepplinger Leopold Werner
Mizelli Herbert
Wurm Johann
Andrews Melvyn
Deutsche Voest-Alpine Industrieanlagenbau GmbH.
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