Specialized metallurgical processes – compositions for use therei – Processes – Producing or treating free metal
Reexamination Certificate
1998-12-28
2002-07-09
Andrews, Melvyn (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Processes
Producing or treating free metal
C266S160000, C266S172000
Reexamination Certificate
active
06416566
ABSTRACT:
The invention relates to a process for the production of liquid pig iron or liquid steel pre-products from charging substances comprising iron ore and fluxes and at least partially containing a portion of fines, wherein the iron ore is directly reduced to sponge iron in at least two reduction stages by the fluidized bed method, the sponge iron is melted in a melt-down gasifying zone under the supply of carbon carriers and an oxygen-containing gas, and a CO- and H
2
-containing reducing gas is produced which is injected into reduction zones of the reduction stages, is reacted there, is withdrawn as a top gas and optionally is supplied to a consumer, and a plant for carrying out the process.
A process for the reduction of ore with subsequent melting is known for example from EP-A-0 594 557. With this known process, in accordance with a preferred embodiment, reduction is carried out in two locally separated reduction zones connected in series, wherein the reducing gas exiting the first reduction zone is supplied to the second reduction zone, which is connected to precede the first reduction zone in the direction of flow of the fine ore, hence in counter-flow, and from there under compression is supplied to a preheating zone. Each of the two reduction zones has an upper section in which fine solid particles are reduced in a fluidized bed and a lower section to which coarser solid particles descend and in which they are reduced in a flown-through fixed bed.
Hereby, advantages result as compared to single-stage direct reduction, i.e. to direct reduction utilizing only a single reduction zone, said advantages consisting above all in a low consumption of reducing gas, namely for the following reason: technical reduction processes require a reduction temperature of at least 750° C., so that there inevitably results a minimum temperature of the reducing gas—when exiting the reduction zone—of 750°.
Since for technical reasons it is not admissible for the reducing gas from the melter gasifier to have temperatures in excess of 950° C., only a temperature gradient of roughly 200° C. is available, meaning that only roughly ⅓ of the sensible heat of the reducing gas can be utilized. To be able to maintain the above-indicated temperature level, it would be necessary with a single-stage reduction process to utilize reducing gas in an amount several times the amount required for reduction. This would result in insufficient exploitation of the reducing gas and hence in a high level of coal consumption in the melter gasifier.
Although this known process has proved its value, different degrees of reduction may result with the fine-grain fraction and the coarse-grain fraction of the iron ore when processing ores of different grain sizes, that is, when processing ores having a slightly higher portion of fine ore (e.g. run-of-mine ore). Remediation is difficult, as it is not possible with this known process to adjust the retention time of the fine-grain fraction independently of the retention time of the coarse-grain fraction of the iron ore in the reactor vessels.
With the known process, the completely reduced fine ore portion from the reduction zone arranged to immediately precede the melt-down gasifying zone is charged to the melt-down gasifying zone separately from the coarse ore portion, namely at the height of the fluidized bed forming above the fixed bed of the melt-down gasifying zone. Hereby, conveying-out of the fine-grain fraction along with the reducing gas generated in the melt-down gasifying zone is avoided. If the fluidized bed becomes overloaded with the charged fine-grain fraction, breakdown of the fluidized bed and subsequently damming-up of gas may ensue. This results in eruptive outbreaks of gas. Hereby, the gasification process for the carbon carriers and the melt-down process for the reduced iron ore, that is the sponge iron, is markedly disturbed. Uncontrollable fluctuations in the pressure and quantity of the generated reducing gas and formation of a reducing gas having a reductant composition which is disadvantageous to the reduction process may ensue.
From KR patent application 94-38980, a process of the initially described kind is known in which in the reduction zone arranged to imnmediately precede the melt-down gasifying zone the prereduced fine ore portion is discharged by means of the reducing gas and supplied to a separate fine ore reduction zone. From the latter, the completely reduced fine ore is also conducted to the fluidized bed zone in the melter gasifier, as according to EP-A - 0 594 557, so that, here, the disturbances already described above may occur in the melter gasifier.
In accordance with KR patent application
94-38980
, the ore is prereduced in a first reduction zone, with the fine ore portion and the coarse ore portion being reduced together in a single reduction zone. This results in the disadvantages described in connection with EP-A - 0 594 557, namely in nonuniform degrees of reduction of the fine ore portion and of the coarse ore portion in this reduction zone.
The invention aims at avoiding these disadvantages and difficulties and has as its object to provide a process of the initially described kind as well as a plant for carrying out the process, by which not only a uniform reduction of the fine portion and coarse portion of the ore is feasible, namely in a reduction process which, in order to achieve good gas exploitation of the reducing gas, is a multiple-stage, i.e. at least two-stage, reduction process. In particular, disturbances of the melt-down process and of the production process for the reducing gas in the melt-down gasifying zone are also to be avoided herein.
With a process of the initially described kind, this object is achieved in accordance with the invention in that:
each of the two reduction stages is provided with two separate fluidized beds, wherein in a first reduction stage the iron ore by aid of the reducing gas is fractionated into at least two fractions having different grain size distributions each, namely into at least one coarse-grain fraction and at least one fine-grain fraction,
each fraction is reduced by the reducing gas in a separate fluidized bed, wherein
the reducing gas maintains a first fluidized bed containing the coarse-grain fraction and separates the fine-grain faction from the same,
and wherein, further, reducing gas is additionally introduced into the further fluidized bed directly, in an amount and/or chemical composition such that reduction of the fine-grain fraction in this fluidized bed to a predetermined degree of metallization within a predetermined period of time is ensured, and
reduced iron ore is discharged both from the first and from the further fluidized bed and
the fine- and the coarse-grain fraction reduced in the first reduction stage are further reduced in a further reduction stage operating in the same manner as the first reduction stage and from the last reduction stage the fine-grain fraction is introduced into the melt-down gasifying zone while being agglomerated by provision of oxygen, preferably by means of a burner, and the coarse-grain fraction is fed directly into the melt-down gasifying zone gravitationally.
The charging of a reduced fine-grain fraction to a melt-down vessel by means of a burner is known per se from KR patent application 92-27502. But here, reduction by the reducing gas is effected in a single stage and melting down of the ore that is only prereduced in the single-stage process takes place by the so-called “in-bath” method. In accordance with this method, only a metal melt covered by a molten slag, without a fixed bed and without a fluidized bed, is present in a reactor vessel. The charged coal gasifies in the slag layer in which the charged prereduced ore is also completely reduced. However, the reduction process takes a completely different course than with the process of the initially described kind and the process in accordance with the invention, as, in prereduction, reduction of Fe
2
O
3
by means of CO and/or H
2
is, at the most, only carried to
Kepplinger Werner Leopold
Kim Yong-Ha
Lee Il-Ock
Park Moon Duk
Schenk Johannes
Andrews Melvyn
Ostrolenk Faber Gerb & Soffen, LLP
Voest-Alpine Industriean-lagenbau GmbH
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